I always thought that deploy keys are read-only. I can't understand why one would need a special interface to add a read-write key that is the same as any other

I always thought that deploy keys are read-only. I can't understand why one would need a special interface to add a read-write key that is the same as any other key you add manually. Iirc only the owner can create deploy keys, so it wasn't a feature aimed to teams either.