Well in some cases it really is more efficient.

    [func(x) if x in collection if cond(x)]

makes a single pass over the data and gives you a list, but

    list(map(func, filter(cond, collection)))

makes two passes and requires some extra function calls.

I think the real reason is perceived legibility on the part of the Python core devs. I seem to recall a document from a while ago in which GvR himself came out in favor of list comprehension style. "Explicit is better than implicit".