Because when they started developing Discourse, it was the best thing around.
If tney were to do it today, I’d guess that the only thing they’d do differently might be to use docker-compose rather than their own custom launcher commmand that builds and launches docker images.
You must be on a different internet than I am. From everything I see, most everyone who manages software on more than, say, 5 servers, is using some kind of container to manage things. Increasingly developers run stuff on their laptops in containers to see that versions of everything is kept consistent.
Even managing a Discourse/rails/ember development environment on a single laptop is something of a challenge.
That’s true. If you want a forum that you can use without Docker, you should not use Discourse.