Original stable diffusion wasn’t trained by individuals, but clearly the current progression of the software is largely community driven. All sorts of new tech and add-ons for it, huge volumes of community trained checkpoints and Lora’s, and of course the interfaces themselves like automatic1111 and vladmatic.
And it’s something you can run yourself offline with a halfway decent graphics card.
Depends, I was mainly active on small subreddits that were focused on things I was interested in. Here those small subs don’t exist yet (or are very inactive), but the lower overall user count means I’m interacting with a lot more communities than I would on reddit.