The fly in the ointment is that they control the software and updates to that closed software so can short circuit that with appropriate pressure.
The tricky part is keeping it from being "permitted" by a crappy contract of adhesion. Banning it entirely would make it very difficult to buy/sell backup services...
For example, suppose the government demands constant access to your core database. You don't need to invent any new algorithms for that, you might just make an SQL user and a firewall exception and call it a day.
Similarly, If you have a messaging client, you don't need complex R&D to steal the "end-to-end" keys.