That's not deliberate foot dragging. Asus, Acer, etc all announced 4k 120 HDR monitors last spring built around prototype panels from AUO with a mid summer ETA based on when AUO said they'd be transitioning to volume manufacture of the panel. Based on the latest slip of the release date, AUO still hasn't been able to solve whatever the showstopper problem has been preventing them from actually starting volume production of the panel. Some part of doing so (I'm guessing the 384 zone HDR) has proven difficult enough industry wide that none of the other panel makers (eg Samsung, LG, etc) have spoken publicly about such a design in their product lineups.
Yeah but the HDR panels are another story. There does seem to have been some kind of foot dragging/fuck up around 4k+120hz in general. I mean DP 1.3 is a standard from 2014 that allows 4k120hz, but afaik no one ever built a DP1.3 monitor, and we're already on DP1.4, which has also never been built. And we do know that lots of LCD panels, including many/most TVs and possibly nearly ALL current LCD panels, support and even sometimes natively(in the case of TV panels) run at 120hz. The issue does not seem to be panel response times or supported refresh rates.