What they've done with the "disable" option is enable a compatibility support module for UEFI to present a faux-BIOS to the operating system. The point of a CSM was to provide backward compatibility to legacy operating system that have no idea how to talk to UEFI, but can interface with BIOS.
So all you're doing is using UEFI and also a fake BIOS layer. But they call this "disabling" UEFI. Hence it's a big fat fucking lie. The things liars tell people who they think are stupid. So, you know, you should be a little pissed at people who think you're a moron that you need to be lied to.
Ohhhhh but we were just trying to make things easier to understand, we were just trying to be nice!
Well, guess what? Go fuck yourself. Stop being nice. Try being honest.