I will post a separate answer that applies to duplicate information in language in general. In most normal sentences, there are many parts that could be left out without making the sentence unintelligible, because there are often several clues that point to the same interpretation.
I killed him because he killed my
I killed him; he killed my father.
That the because-clause would indicate the motive for killing "him" is clear even without the word "because", because it can be inferred from context that this must be the motive with reasonable probability. That is why the second sentence is still perfectly intelligible on its own. Any aspect of a sentence can be a clue: word order, case, the choice of one word over another, the addition of adjectives and adverbs, expressing the agent of a verb instead of using a passive form, etc., etc.; and in the context of the sentence or in the real world there are always clues as well.
So is the word "because" merely a burden that should be cut out for efficiency? No. There are two reasons:
Oftentimes, the listener misses some part of a sentence, because of noise, distraction, et cetera. In addition, the speaker could make a small mistake or be a bit unclear. The extra information in these "duplicate" clues is an excellent instrument for the listener to repair these lapses and prevent ambiguity. Especially long sentences with many clauses take a toll on the listener or reader and tax his concentration, in which case he will be happy with extra clues.
Even when the listener does not need to make any repairs to what he hears, it takes less effort to understand a sentence if one has several clues. Conciseness can be taxing. The more "inferrable" words that are stated explicity, the less work the listener has to do.