Learning how to ask a good technical question is an extremely valuable skill in and of itself, and StackOverflow is one of the few ways you can learn to do it. Just as you've said - if you ask a coworker (or a real person in general) they'll work with you to dig the question out, but they aren't really teaching you how to ask it more efficiently in the first place. They aren't giving you specific feedback on your question.

StackOverflow on the other hand will often give you an actual critique of your question. That criticism can be really frustrating, but it's often good for you (it has been for me). Often the problem is a problem only because of how you perceive the problem space, or you're wrong about fundamentals. Other times you're not including important details because you didn't know they were important and just having that pointed out can help, or this problem is of a known form with a known solution - you just didn't know the "magic words."

There's even something to be said for forcing people to learn a bit about the community before jumping into it. As annoying as that is and as much as it is an on boarding obstacle - it helps people work together. The on boarding process for a driver's license sucks and puts up tons of barriers, but with good reason.

I don't disagree with anything you've said, or deny that super rude and unhelpful behavior occurs there, I just want to say that some of the "bugs" of StackOverflow are probably "features."