The explanation is that the platform firms operate with a high level of market power, which is another way of saying that they benefit from monopoly or near-monopoly effects that make them relatively immune from things like what their customers want.

This is actually textbook monopoly stuff, well established in antitrust literature and well understood by regulators: when you see a firm institutionalizing how to defend criminal activity as a part of their business model, it's a big flag that said firm probably has some kind of immunity from how healthy, regulated markets operate. Why America has decided not to prosecute corporate criminals anymore (given that at various points in its history it was actually pretty good at this) is the really interesting question of our time.