It's my understanding that UEFI actually comes up directly into long mode?

"UEFI firmware performs those same steps, but also prepares a protected mode environment with flat segmentation and for x86-64 CPUs, a long mode environment with identity-mapped paging. The A20 gate is enabled as well."

- https://wiki.osdev.org/UEFI

Unfortunately most BIOS services are only available in real mode, so it's often necessary to switch back and forth.

This inadvertently triggered my A20 gate rage.