People like to moan about Zimmer (and I do loathe his scores with a passion) but he just gives the studios what they demand: A score that fits a deadline, certain quality standards and the budget. If it weren't for Zimmer someone else would have filled his role. It's just what happens to a product or industry that is past its heyday. The same happens, for instance, within the garment industry. Once a (non luxury) brand is well established it "optimizes" the costs of its clothes until people complain that the quality has become unacceptable.