I’ve already written about the redundancy of the reason is because, but I’ve noticed that many people are also curious about whether the reason why is correct grammar. Both the reason is because and the reason why have something very basic in common: they’re entries for the category of the redundancy category.
The reason is already the why, and the why already means the reason. When you ask why, you’re asking for the reason, and when you ask for the reason, you’re asking for the why. You can slice it any way you want, but it still comes out looking like a redundancy. Saying the reason I wanted to do this was to… is sufficient. There’s no need to say the reason why I wanted to do this was to….
Don’t even get me started on the whole the reason why is because thing. That’s a triple redundancy that would need a category of the redundancy category of the redundancy.