Just to add another one-
The wings are very long and droop somewhat, hence the outriggers.
A low wing would not be able to droop as much, meaning more strength = more weight = less payload etc etc
Also, due to the wing length, even applying outriggers on a low wing would make the a/c very ungainly and difficult to land in crosswinds without losing engines etc.
These are secondary considerations, although all things would have been considered to end up with the best compromise of a design.
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