Maybe because knowing or being able to talk in a language itself is not enough to be able to teach others

Perhaps you have had a bad experience with a native language speaker who couldn't help you learn their language? I-talki is full of native speakers who are only too willing to give their time and energy to help others - just ask your question here and there are many of us who will do our best to help you.

Dear Ahmed! I am emphasizing your answer because it really is that. Thank you for answering!

maybe because the foreigners are stuck to the formal language and very limited number of words it may be too for some pronouncing and accent issues