Depends where you look... games consoles have pretty huge leaps from generation to generation, although more recently the cycles have been longer.
That said, it would help if it was a clear improvement at all. If Rift S had ended up with the reverb screens and a slight improvement in FoV to say 110-120 degrees then while some would still complain of course I think the majority would be happy with the improvements.
As it stands it’s more of a v1.1 - the biggest improvement seems to be in ease of use with the insight tracking. The lenses give a small upgrade in clarity, the screen a small bump in resolution but the trade offs leave it inferior in some aspects - tracking possibly not as comprehensive, speakers not as good, no juicy OLED blacks, no physical IPD etc etc.
If the rift S had come out a year after then it would be comparable to an incremental phone upgrade, but given it’s been just over 3 years I think people were disappointed it isn’t just a bit more of a clear improvement over the original, while also increasing the price from $350 to $400.
More than anything I think you are just seeing people upset that the proper Rift replacement they were hoping for is a long way off. Personally I would guess to see that in around 2-3 years if oculus are still interested in the higher end PC market at that point, which they may not be depending on how the quest/rift S figures stack up.