This is clearly for sites that require more than a fraction of a droplet to run. Just because WordPress can be run on a tiny instance doesn't mean that every WordPress user does -- some sites are actually popular.

Stick CloudFlare as a CDN and configure it, enable some caching plugin on WP and you'll need some serious traffic to saturate that small droplet.

You could host several WordPress sites on a free tier AWS EC2, too. Where things get a little more complicated is when you're getting real traffic and want to be fault tolerant and redundant.

RDS is here because keeping your database on the same server as your web server is not ideal at scale.

EFS is here because at some point you want to scale horizontally and it's one method to share underlying code (and perhaps cache).

ELB is here because if you have more than one web server, you need a load balancer

And as you scale, you could add services. This guide isn't for anyone who can host a tiny site on a tiny instance. You'd do that in AWS the same way you would with Digital Ocean.