I think they also do a great job of capturing communities and discussions which SO purposely devalues. I imagine a lot of problem solving happens in discord and github now.
It might also be that SO was good for arbitrary and shallow questions, but most problems with more modern frameworks that aren't covered by the docs get domain specific and complex quick.
It might also be that SO was good for arbitrary and shallow questions, but most problems with more modern frameworks that aren't covered by the docs get domain specific and complex quick.