It was FORTH, which most developers really hated. Sometimes the end users even got exposed to bits of FORTH poking out, for example in the syntax for booting.
We really just wanted a nice clean 64-bit BIOS, with all the datatypes 64-bit. The BIOS is pretty decent if you strip out redundant interfaces, segmentation, and never-used functionality. Adding extra functionality to firmware is madness. Firmware needs to initialize key hardware like RAM, load a boot loader, and get out of the way. Firmware doesn't need to be practically an OS.
The old 16-bit BIOS was actually working OK. Sure, it was nasty to program for, but almost nobody had to deal with that.
