t is not a question of "strange decision by AMD" at all. It is a question of very limited AMD ADL API. NVIDIA cards simply have unified GPIO/VID based voltage control functions inside NVAPI, so it is very easy and fast to support voltage control on new cards (within driver allowed voltage control range of course) or even provide voltage control for future cards without even seeing them.
It doesn't apply to AMD. To support voltage control on new cards developers first need to implement low-level I2C aceess support for each new GPI family (which can be troublesome for new GPU architecture), then provide support for each new voltage controller model. That's not the task that can be done without hardware.
Alexey Nicolaychuk aka Unwinder, RivaTuner creator