I've done the self-answer thing a couple of times. Sometimes you just know that someone is going to run into the same problem, but you'll never see the question, and you can preempt it.
I think I've posted on StackOverflow/ServerFault three times in my life. If I've hit the point where I'm posting, I'm desperate and I've probably already spent 8+ hours scouring Google and trying everything I can think of.
If I do end up figuring out a solution, I definitely post it, and I'm glad that SO allows this, otherwise there would still be no answer to some of these questions online... One of these issues previously only turned up a single bash mailing list post from a decade ago with no resolution. Now searching for a few relevant search terms turns up my answer/solution in the top few results for all of them.
I don't care about imaginary internet points, I just figured I'd help the next guy out.
More than once I've solved the problem by the time I am 80% of the way through formulating a question. As long as it's not something trivial I finish and post the answer immediately.
People use sock puppets to do this because although you're correct that it's with the SO guidelines, it feels a bit off, and not uncommon for it to get pushback from those who either don't agree with the guidelines or are not aware of them.
Also, while voting fraud is against the guidelines and actively countered, creating sock puppet accounts is not.
Sometimes the act of writing out a question is enough to spur the right ideas to solve the problem. It's the same as whiteboarding or asking to use someone as a sounding board.
SO actually allows this, Q and A from the same account. Some people use sock-puppets though.