Sure, Clipper was a disaster, but we've learned a lot about encryption since 1998. I still think key escrow and gov't backdoors are probably a bad idea, especially when you look at the US's privileged position in the internet, which should really be a global or jurisdiction-free space. However, I don't understand why it would be so much harder to protect these keys than the update signing keys that Apple, Google, Microsoft, etc (not to mention every app author including Facebook) already have to protect in order to prevent malicious actors (including nation states) from trivially bypassing all security protections by pushing a signed update to the end-user device.

Honestly if your security model involves hiding from the FBI/NSA, you should not be using a cell phone to do your encryption/decryption. That device runs closed-source blobs and can be remotely configured, accessed, and updated by (at least) your carrier and the device manufacturer.