Banks are like oil. Even if we have all the means and alternatives to survive and live without it. There are a lot of people that would lose bucks of money if such alternatives rised and killed oil for good. So for that same reason, Facebook and other companies can also come to play on the crypto and money world, but in the end, the major banks will always make sure they just play on a limited zone and don't reach much on that area they already fully control.