A theory I have is that it is due to unmet expectations. I haven't kept up with any of the marketing or the source material, just watched the show. I thought that while the show could probably have stood to be a season or two shorter, that this final season was them sticking the landing pretty well.

Then, I went and saw the complaints. And then, I checked out how the season was marketed, and they absolutely were selling it as if this season was going to build to a no holds barred apocalyptic final battle. What we got was much more subdued and focused on character moments. If I'd been inundated with that marketing, I'd have been disappointed too. If I'd been invested in Gen V, i would have been disappointed.