I know this thread is a little old, but I thought I would offer my two cents for why this may happen. I am not actively in a class (I start in a couple days, but it is not formal and will not be graded or go on a transcript), but I imagine that when people come here for help or answers to their questions, it is much like students of other foreign languages and unfamiliar cultures.
I speak a fair amount of Spanish and just conversationally in a couple other languages, and I actually do ask strangers for help. "Buenas tardes. Como esta usted hoy? Si? Trabajando duro? Hey--como se dice __________?" How do you say __________? What does X mean? Why do they use the word Y in Z region? Where else?
The thing is, I can typically guess whether or not someone is a native Spanish speaker, and I might be able to guess where they are from. And of course, Spanish speakers are everywhere in the US. They are plentiful. This is part of why other languages I know a little of are difficult to pick up. It's not easy to find a general forum for, say, native Japanese speakers and then be able to communicate with them and ask questions if you are just starting out.
ASL students looking to have their homework done should probably find other study tools, but I think it's sort of natural that hearing "seekers" if you will turn up here for help with aspects of a language that is foreign to them and more likely to be native to many members here. These people--me, we--benefit from those of you who are bilingual. You know the language we're trying to learn, but you also communicate with us fluently in written English. It's difficult to resist the temptation to ask questions.
I have randomly bumped into and then identified fluent ASL users a total of three times (to be fair, two out of those times users were en masse) in my 23 years. That's not a lot compared to the speakers of Farsi, Mandarin, Hebrew, German, etc. I have met and identified.
Maybe this group should start a forum of its own: Wannabe ASL Users United.
Just my thoughts.