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.