A traditional rule holds that the construction the reason is because is redundant, and should be avoided in favor of the reason is that. The usage is well established, however, and can be justified by analogy to sentences in which so that follows purpose, as in His purpose in calling her was so that she would be forewarned of the change in schedule. A similar construction employs the conjunction when after the noun time, as in The last time I saw her was when she was leaving for college. You may find these constructions inelegant, however.
