Why many actress wont act in their mother tongue movies?

I have seen many actress acting in other language movies rather than acting in their mother tongue movies. If its their mother tongue, it will be simple for them to understand and act easily however many wont do that. What could be reason behind that?? Is it because of remunaration? Lets take either tollywood or kollywood, many actress belong to other state only. Whereas male actor act in their mother tongue language movies except very few. Is it because of acting skills? If it is because of acting skills, then they can act in their mother tongue movies too.
For eg: Anuska shetty, trisha, nayantara and many more.
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