I think you nailed it. I try to answer questions on SO when I have spare time. But that's mostly because of the massive value I've gained from the site. Most of the time it's not even asking questions, but looking at great answers to questions that have already been asked.

If I continue to get the same value from SO, I'm happy to keep answering questions where I can and they're free to profit off that in any way they choose as long as everything remains public.