Back in those days, it was never really as simple as "sftp my .php file into a folder and call it a day". If you were on a shared host, you may or may not have access to any of the PHP config, needed for things such as adjusting memory limits (or your page might not render), which particular PHP version was available (limiting your available std lib functions), which modules were installed (and which version of them, and whether they were made for fastcgi or not). Scaling was in its infancy those days and shared hosts were extremely slow, especially those without caching, and would frequently crash whenever one tenant on that machine got significant traffic. If you were hosting your own in a VM or bare-metal, things were even worse, since then you had to manage the database on your own, the firewall, the SSH daemon, Apache config files in every directory or Nginx rules and restarts, OS package updates, and of course hardware/VM resource constraints.
Yes, the resulting 100-line PHP script sitting on top of it all might be very simple, but maintaining that stack never was (and still isn't). Web work back then was like 25% coding the PHP and 75% sys-admining the stack beneath it. And it was really hard to do that in a way that didn't result in customer-facing downtime, with no easy way to containerize, scale, hot-standby, rollover, rollback, etc.
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I'd probably break down this comparison (of LAMP vs modern JS frameworks) into questions like this, instead:
1) "What do I have to maintain? What do I WANT to maintain?"
IMHO this is the crux of it. Teams (and individual devs) are choosing JS frameworks + heavy frontends because even though there are still servers and configurations (of course), they're managed by someone else. That abstraction and separation of concerns is what makes it so much easier to work on a web app these days than in the PHP days, IMO.
Any modern framework now is a one-command `create whatever app` in the terminal, and there, you have a functioning app waiting for your content and business logic. That's even easier than spinning up a local PHP stack with MAMP or XAMPP, especially when you have more than one app on the same disk/computer. And when it comes time to deploy, a single `git push` will get you a highly-available website automagically deployed in a couple minutes, with a preconfigured global CDN, HTTPS, asset caching, etc. If something went wrong, it's a one-click rollback to the previous version. And it's probably going to be free, or under $20/mo, on Vercel, Cloudflare Pages, Netlify, etc. Maybe AWS Amplify Hosting too, but like Lambda, that's a lot more setup (AWS tends to be lower-level and offers nitty-gritty enterprise-y configs that simpler sites don't need or want).
By contrast, to actually set up something like that in the PHP world (where most of the stack is managed by someone else), you'd either have to find a similar PHP-script-hosting-as-a-service like Google App Engine (there's not many similar services that I know of; it's different from a regular shared host because it's a higher level of abstraction) or else use something like Docker or Lando or Forge or GridPane to manage your own VM fleet. In the latter cases you would often still have to manage much of the underlying stack and deal with various configs and updates all the time. It's very different from the hosted JS world.
The benefit of going with a managed approach is that you're really only needing to touch your own application code. The framework code is updated by someone else (not that different from using Laravel or Symfony or Wordpress or Drupal). The rest of the stack is entirely out of your sphere of responsibility. For "jamming" as an individual or producing small sites as a team, this is a good thing. It frees up your devs to focus on business needs rather than infrastructure management.
Of course, some teams want entirely in-house control of everything. In that case they can still manage to their own low-level VMs (an EC2 or similar) and maintain the whole LEMP or Node stack. That's a lot more work, but also more power and control.
A serverless func, whether in JS (anywhere) or PHP (like via Google Cloud Run), is just a continuation of this same abstraction. It's not necessarily just about high availability, but low maintenance. You and your team (and the one after them, and the one after that) only ever have to touch the function code itself, freeing you from the rest of the stack. It's useful the same way that being able to upload a video to YouTube is: You can focus on the content instead of the delivery mechanism.
2) Serverside resource consumption
It's not really true that "PHP scripts don't consume any resources (persistent processes, etc.) when they're not being used", any more than a JS site or serverless func isn't consuming resources when they're not being used. Both still require an active server on the backend (or some server-like technology, like a Varnish or Redis cache or similar).
Neither is really an app author's concern, since they are both hosting concerns. But the advantage of the JS stuff is that it's easier and cheaper for hosts to containerize and run independently, like in a V8 isolate (for Cloudflare Workers). It's harder to do that with a PHP script and still ensure safety across shared tenants. Most shared PHP environments I know of end up virtualizing/dockerizing much of the LAMP stack.
3) Serverside rendering vs static builds vs clientside rendering
As for serverside rendering vs static builds, the article doesn't really do a fair comparison of that either. This is a tradeoff between delivery speed and dynamicness, not between PHP and JS.
Even in the PHP world, the PHP processor itself offered caching, then frameworks like Wordpress would offer its own caching on top of that, then you would cache even the result of that in Varnish or similar. That essentially turns a serverside rendered page into a static build that can then be served over a CDN. This is how big PHP hosts like Pantheon or Acquia work. No medium or big size would make every request hit the PHP process directly for write-rarely, read-often content.
In the JS world, you can also do serverside rendering, static builds, clientside renders, and (realistically) some combination of all of those. The difference is that it's a lot more deliberate and explicit (but also confusing at first). But this is by design. It makes use of the strength of each part of that stack, as intended. If you're writing a blog post, chances are you're not going to edit that more than once every few weeks/months (if ever again). That part of it can be statically built and served as flat HTML and easily cached on the CDN. But the comments might trickle in every few minutes. That part can be serverside rendered in real time and then cached, either at the HTTP level with invalidations, or incrementally regenerated at will. And some things need to be even faster than that, like maybe being able to preview the image upload in your WYSIWYG editor, in which case you'd optimistically update the clientside editor with a skeleton and then verify upload/insertion success via AJAX. The server can do what it does best (query/collate data from multiple sources and render a single page out of it for all users to see), the cache can do what it does best (quickly copy and serve static content across the world), and the client can do what it does best (ensure freshness for an individual user, where needed).
It is of course possible (and often too easy) to mis-use the different parts of that stack, but you can say the same thing about the PHP world, with misconfigured caches and invalidations causing staleness issues or security lapses like accidentally shared secrets between users' cached versions.