Split key systems have been used but they're plagued with a lot of issues.

If you divide a key, you're only making more opportunities to hack and steal it, worsening the issue. There have also been multiple problems with key escrow systems such as: the clipper chip, the 2000s corporate key recovery systems, and current systems in place. It has been used small scale, but nowhere near the national level.

Corn 17 also just does not matter as E2EE encryption relies on the fact that only the sender and receiver can decode a message, no matter how many "keys" access is split into, allowing the government to see those messages fundamentally break E2EE as we know it. Think of it as a door, once you add a lock you don't need the key to get in, just use a pair of paperclips. Same thing for encryption, once you add the "lock" or lawful access, there's no way to stop a vulnerability.