But remember Hanlon's Razor: "Never attribute to malice that which is adequately explained by stupidity" (https://en.wikipedia.org/wiki/Hanlon%27s_razor).
UEFI smells like it was designed by a committee, so the value it adds (if any) seems far outweighed by the added complexity (and corresponding security challenges) it creates... to paraphrase Douglas Adams: (and replacing the word "Universe" with "BIOS":)
“There is a theory which states that if ever anyone discovers exactly what the BIOS is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable... There is another theory which states that this has already happened...” <g>