"The reason is because" means the same thing as "The reason is [that]", but it does NOT follow that because is redundant or incorrect. Instead, because is playing a non-semantic role in the larger sentence.
This is easiest to understand in the context of spoken language, where the because would be acting as a filler word. Imagine stretching it out further: "The reason is, um, because, well, like, ..." It's perfectly normal in English to use semantically duplicative words as filler, instead of um/er/uh.
In written language, because is instead used (or not used) to improve rhythm and flow. Consider the following two examples, both from writers whose stylistic chops are impeccable:
“If the fellow who wrote it seems to know more of my goings and comings than he could without complicity of mine, the reason is because he is a lovely old boy and quite took possession of me while I was in Boston”
[1915, Robert Frost]
“… one of the reasons why I am not particularly well read today is because I have spent so large a part of the last twenty years rereading Dickens and Jane Austen.”
[1932, Alexander Woollcott]
(both quotations copied from this article which contains a good deal more descriptive analysis of this construction)
In both cases, omitting the because (or substituting that) would make the clause transition jar. In the latter case, with the caused-state in between the reason and is because, the because also serves to remind the reader of the overall structure of the sentence.