Why doesn't the PLAAF insist on stopping using HUDs? New generation helmets, especially those on the F-35.
HUDs are relatively low in weight in context of the full airframe so they have barely a penalty on the aircraft's weight overall -- more importantly, compared to HMDs, HUDs are able to pump out higher quality imagery for the same mass/weight.
It essentially means that with HUDs, you get the best of both worlds -- the ability to fly without needing a relatively heavier HMD (compared to regular flight helmet) all the time even for sorties were HMDs don't matter, as well as being able to wear the HMD for sorties where you think they are needed (reducing cumulative load on the pilot's neck), while still having the HUD as both a backup and a higher resolution display than what the HMD can put out.
Going without HUDs means you force your pilot to fly with a HMD for every sortie, and it also means you are more limited in resolution in from the frontal perspective/angle of the HMD's display compared to what a HUD can offer.