The major problem is, simply, nobody plays some of these modes. Finding a server with enough people on it to make it a game is just about impossible for some of em, even the cool sounding ones like TeamHunters. Even if you make it onto a server, chances are you will be on the sucky team. Maybe it's just me, but Tribes multiplay has always been a study in one team kicking the crap out of another on a regular basis. It's not a game issue, I suppose, so much as it is a player issue.
Teams are really good, or they really suck.
That's just the way it is. However, the little extra that pushes it to five-sword status is the support. Now, there's a school of thought that says there should be no need for patches, that games should be shipped when they're done. While I agree with that school of thought on a philosophical level, it fails to recognize the real world realities of budgeting and bosses. Sometimes you just HAVE to push it out the door and hope your development team can finish it up via patch.