If we consider information to be safe if we encrypt it (e.g., text in a file, encrypted with modern strong encryption), would it be safer (as in harder to crack) if we then encrypted the encrypted file, and encrypted the encrypted^2 file, etc.? Is this what strong encryption already does behind the scenes?
Mathematically yes, but in the real world, it’s probably not much safer.
Imagine that you’ve got an unpickable lock on the front door to your house. You’re asking about putting another door with another unpickable lock in front of it.
Great, sure, but we’re talking about a world where most people get in not through picking the lock, but by someone leaving the backdoor open, or hiding keys under the doormat.
Disclaimer: I’m not making any claims about household break-and-enters. It’s just an analogy.
Using multiple layers of different crypto helps add backdoor resistance