Why did SO decide to do that to us? to not invest in ai and then, iirc, claim our contributions their ownership. i sometimes go back to answers i gave, even when answered my own questions.

Decide to do what?

SO didn't claim contributions. They're still CC-BY-SA

https://stackoverflow.com/help/licensing

AFAICT all they did is stop providing dumps. That doesn't change the license.

I was very active, In fact I'm actually upset at myself for spending so much time there. That said, I always thought I was getting fair value. They provided free hosting, I got answers and got to contribute answers for others.