Jak mi již potvrdili rodilci, může to být správně, ale mě to prostě pořád nejde na jazyk Našel jsem i vlákno na ELL: https://ell.stackexchange.com/…-why-arent-y :

“Why don't you be more sociable?” can be correct, if it refers to one, particular, occasion.

“Why aren't you more sociable?” would be correct if it is meant generally.

Lze to použít třeba u třetí osoby? Tak mi to přijde prostě divné (Why doesn't he be?).

Lze to použít třeba u třetí osoby? Why doesn't he be?

Ano, lze.

• A: Several people have tried to chat to him but he just sits in the corner moping. Why doesn't he be / isn't he being / isn't he more sociable?
• B: Well his grandma has just died and he's taking it rather badly, I'm afraid.

Díky Dane, pro mě docela novinka slyšet “doesn't he be”.

Takže jestli to chápu: Why isn't he more sociable? (proč obecně, dlouhodobě není..) Why doesn't he be more sociable? (proč teď není)

Není mi úplně jasný vztah doesn't he be / isn't he being , gramaticky.

I don't necessarily agree with the answer given on stackexchange. “Why don't you be more sociable?” can also be used in a context where the “being sociable” is a regular or repeated occurrence.

• I always invite you along when I go to the pub on Friday evenings but you never want to come. Why don't you be / aren't you more sociable?

“Why aren't you more sociable?” can also be used in the context of “right now”, though it's true that it would usually refer to a general habit. However, if someone is generally not sociable, that would usually be the case on any one particular occasion too, unless there's something in the context to indicate otherwise.

• That lady next to you is trying to strike up a conversation with you, but you seem to be ignoring here. Why don't you be / aren't you being / aren't you more sociable?

The matter of whether we're talking about a regular, general habit or a present-time situation is determined by the context, not by the form of the verb.

It may also be the case that “be sociable” can be felt to be either stative (have a sociable temperament – “he's not very sociable”) or dynamic (act in a sociable way – “he's not being very sociable”).