I started it as a way to learn things. Mostly picked questions that were on the edge of my understanding, researched the problem for myself, and then tried to provide clear and detailed answers. So I got a lot out of it too.
My view for when SO started to decline is also similar to yours - being flooded with poor quality questions. And on average people asking questions became more arrogant, put little effort in, and demanded the whole place to change so they can paste their broken code and have someone fix it for an upvote.
So I think I naturally and slowly drifted away from using SO. However, publicly stated reasons for SO's downfall often proclaim there was something wrong with people who answered questions. That they were rude or were "gatekeeping". I always feel alienated reading those, since it's very different from how I experienced the site.