Rather question. Not the issue. Why not use OPTEE in UEFI's SMM module?

[P1119r1m]

I am sorry for asking question here, but I have no luck to find another place.

I know that boot flow in current realization is like that:
ARM-TF -> OPTEE-OS -> UEFI ... -> LINUX.
While reading documentation about UEFI, I found that it contains such a module as SMM (System Management Mode), which is running at the highest priority exception level of a processor.
So, I'm just wondering if it possible to run or even inbuilt OPTEE-OS inside of SMM.
Is it a better way to secure boot system?

I understand, that question may looks a bit confusing, but anyway I will appreciate any mentions.