(A) Apple made these changes (that effectively keep court ordered inspections blocked) in response to earlier court ordered inspections (Apple assisted in something like 70 cases)
(B) The technology itself can be outlawed (encryption falls under war weapon technology and is restricted in export and other categories).
What is to stop all devices from adding “self-destruct” technology?
They could pass a law that prevents device makers from putting encryption on the device, but they wouldn't be able to prevent users from putting their own encryption on there. PGP, GPG, VeraCrypt - there are a host of commercial and open source encryption tools. (Personally, I would tend to trust the open source tools more - commercial tools are more susceptible to government pressure to put in back doors.)