People hate Arena because they don't like sitting out. I know that when I connect to the server, I want to play. I don't want to watch people play.
Unless you're an absolutely amazing player, you will invariably have to sit out a few rounds. That's annoying. It's especially annoying when people decide they don't want to cap the point but hunt down that last player who just won't die, thereby extending the round longer than it should be.
I don't like Arena; I think the implementation is crappy. Dealing with no respawn is fine, but going whole rounds without even playing? No thanks.