What I like about bios is how simple stupid it is. It reads a bunch of bytes in and boom and starts running them. Partition tables and multiple stages, yes that is the convention but you dont have to adhere to that if you dont want to. Having to change into long mode, yes that is an important wrinkle I give you that. But either way, the design is so simple that you could write a little hello world mbr-program with a hex editor. It's a handful of bytes.

Ok contrast that with UEFI. There are FAT boot partitions and PE executables and what not. That's a lot more complexity.