That's the reason why/because/that - Qual a diferença?

That's the reason why he wants to become an American citizen
That's the reason because he wants to become an American citizen
That's the reason that he wants to become an American citizen
The reason he wants to become an American citizen is that he considers to live there.


Gostaria de saber qual a diferença entre as estruturas, se são todas possíveis, ou se todas estão corretas do ponto de vista gramatical

thanks, love you all