But I just saw a 20-something bragging about how he was using it with clay to create personalized apps.
You have to remember that a lot of people in the industry have ass-backwards values. A lot of people squee when they see chaos and the more chaos the better. When things are orderly they feel like they are in the Apple '1984' video
https://www.youtube.com/watch?v=ErwS24cBZPc
It's got a lot to do with why Docker is so popular. Instead of deciding that you're going to use a certain version of libc and a certain version of Java and a certain version of MUI widgets, they take joy in having many different partitions of the system slightly different from others in ways that will cause all sort of problem large and small. If you standardized things you could run multiple tenants with 1/10 the resources you'll waste with Docker, in a just world it would mean you crush the Docker-using competition but unfortunately the Docker-users are often backed by VC which can be irrational longer than you can stay solvent.
Lots of Docker fans don't think about what version of libc or java is in their image. They start with a base image, develop code that works there, and release the docker container without ever thinking about it.
If it's an open source project, ignoring bugs that occur outside the official docker build cuts out a lot of work. Inevitably someone with no Linux experience will try to setup Slackware on a raspberry pi to run your project because they read in a forum post that 'real nerds run slackware.' When it doesn't work and they open a bug report, you can spend the next year trying to teach them enough about Linux for them to fix their system and run your project. Or you can come across as mean by saying RTFM. Or you can just avoid all that by pointing them to the Docker image and admitting "I only have the resources to ensure this works in that specific environment."
If it's a corporate project, it safeguards against other devs or someone in IT being foolish. Despite having rules and procedures in place, I've seen plenty of instances where IT or a dev changed something in production environments without warning or announcing it because they thought it would be fine.
My early history with Docker was terrible because it just didn't work for me because I had a slow ADSL connection and any attempt to download images would time out and fail. (I guess reliable downloads are a "call for prices" kind of feature) Later on working at an office with gigabit I found that Docker only increased build times by a factor of 2-10x depending on what I was doing.
I was wanting to build an image sorter last year and wanting to try the danbooru image board software, the git repository says just do
docker compose