What I discovered, decades ago, was that posting questions, or even better, answers, even wrong ones (unintentionally) is a phenomenal way to learn things.

That still holds true. Though it helps profoundly to not insist on being wrong.

Which I try to do. Not always successfully.

I'm as well a long time lurker. Whenever I contribute something, I feel that it should be helpful for many other people out there. This comment probably isn't...

Another reason why people avoid contributing: unwritten social rules. New members often step on people's toes and suffer the consequences. As a result, joining a new group can be intimidating. Better to lurk for a while and gain understanding of what is and isn't normal.