This is the issue. If you encrypt your own, then the software will not be able to use it as it's not a file it expects. So all of the software that you want to use your encrypted files will need to have this type of module.
At that point, I feel like we've opened pandora's box. If every single app had to be able to decrypt/encrypt with your personal key, we just know someone will roll their own and fuck it up for everyone else.
In NT you can have modules that sit between various operations on the file system. It’s how AV works without having to hook into every single application that reads and writes from storage.
There’s no technical reason why this kind of approach couldn’t be applied by Apple for encryption. But it would require relinquishing some control over their platform, so it would never happen.
At that point, I feel like we've opened pandora's box. If every single app had to be able to decrypt/encrypt with your personal key, we just know someone will roll their own and fuck it up for everyone else.