...and Morrowind was a "downgrade" from its predecessor, so why isn't everyone voting for Daggerfall? Is it because it became uncool to hate Morrowind after it was no longer the new game?
Because Daggerfall is old, and came out when gaming was still a relatively niche pasttime. There are simply far fewer people who played it. The demographic gets larger every year, so even if 99% of the people who played Daggerfall thought it was the best game of the series, they're going to be overshadowed by the millions of people who played Morrowind and Oblivion.
In fact, the Bethesda website's news archive goes back to 2001. I don't know whether the site was around longer than that, but it's worth noting that Daggerfall came out in 1996 and Morrowind in 2002. When Daggerfall came out forums were only starting to exist at all. Odds are they had only a small window and a small minority with which to hate Morrowind before being swallowed up by the comparative tide of its fans.