I think there will also be an enormous drop in revenue once the next recession comes. A lot of loss-making companies, aiming to grow as fast as possible using VC money, use cloud providers because it's one less thing they have to learn how to do. If they have an actual business model, like Dropbox, they eventually self-host. If they don't, and didn't really expect to have to develop a business model other than "grow really big", then once the VC spigot gets turned off they will shut down.

It is much like the late 90's boom, when a lot of companies were selling banner ads to each other. Even the ones who appeared to be profitable weren't really, because all of their customers were not. Once the loss-making customers of cloud companies go away, the big three cloud companies may find that they don't have a business model either.