We often hear people say things like, “the reason there’s a hole in the screen door is because I tripped over the cat on my way out.” The phrase “is because” should be “is that.” If you wanted to use “because,” the sentence should be phrased, “There’s a hole in the screen door because I tripped over the cat.” “The reason being is” should be simply “the reason being.”

The similarly redundant common expression “the reason why” is generally regarded as standard now, although some people still object to it.