Anyone can come up with a standard in isolation. Getting the relevant people on board and able and willing to support it is the useful bit.
Did they say they'd support it? If they never said they did it seems unfair to criticise. Are you going to support my graphics standard that I just made up?
Except gaming is not that "niche":
1.35 billion PCs worldwide - https://www.statista.com/statistics/610271/worldwide-persona...
47M active daily and 90M monthly users for steam https://www.pcgamer.com/steam-now-has-90-million-monthly-use...
You can think of any number of fantasy scenarios that would make one of the biggest GPU vendors care about your standards, but sadly that is not the world we live in. The world we live in is one where Nvidia has the best game support on the market (far, far better than AMD - let's not even think about Intel here) and therefore anyone who still plays games on a PC will own one of them unless they are some sort of AMD advocate.
At the end of the day, nobody wants to be reading "we don't support this because they're not nice to us". That's going straight back to the linux dark ages of 15 years ago, where you needed to care about all sorts of weird and arcane details to get a functioning desktop system.