How about using GOOGLE? Or YOUTUBE? Or even Grammarly?
There are plenty of tools everyone could use. Even simply reading books and novels would help. Heck, even watching English movies would.
Who has the time to spend giving personal tutorials. And it's not like people would actually pay for tutors just so they could write grammatically correct posts.

but some sources you mention sometimes share language that is not natural or authentic. when I watch movies, sometimes I need more explanation. I'm studying English pragmatics now, and it makes me a little bit confused. so I think it is better to learn from those who own the language.
well, grammatically correct posts is just another stuff probably the other users need.
knowing something doesn't mean you can also teach it. these two are very different.
for example I believe you are Indonesian, can you teach others speak your language?
the time it takes aside, it is always a hard thing. you don't know where to begin, what to tell others and how to simplify it and how much of it to tell them.
but the online resources are prepared by those who are experts in teaching that particular topic. that means it is prepared well enough for different levels to learn that topic. what you need to do is finding a good source for learning.
I always liked Lynda.com videos, although I don't know if they have anything on learning English I have always used their computer related stuff. (... cough .... you can find all of their videos through pirate torrent sites ... cough ....)