It's not for the reasons you think. Which are in rough order:
1) Isn't the best way to decide a National Champion
2) Is subjective, not objective
3) Isn't fair to teams in smaller conferences
4) Rewards teams for softer schedules
5) Doesn't maximize NCAA revenue
Actually most of those are true, but that's not my premise.
The problem is, it was thought the BCS would tidy up a small loophole in which sometimes the top two teams wouldn't play each other, this would make it happen. That's all it was supposed to do. It wasn't supposed to be a playoff. It wasn't supposed to redefine the way the college season was played out, but it did. All of the sudden, the emphasis in college football didn't become "win your conference", it became "win your conference and hope other teams lose and argue against smaller conferences and if you lose, hope your loss is better...". And college football is the worse for it.
One unintended consequence is that the non title BCS games are rendered meaningless. For a few reasons. One is that there is no identity for each. You don't get the same conference champ in each one, half the time that champ goes to the BCS title game. It's not the same (not even close) to have a runner up represent that conference in the title game (i.e. Illinois against USC that one year). It makes it where the SEC champion DOESN'T want to go to the Sugar Bowl, because they failed. If you make the Sugar Bowl out of the SEC, it's because you FAILED in the SEC title game. The Big XII champ has NO desire to make the Fiesta Bowl, because that means they aren't playing for anything. The Big 10/Pac 10 champs the same. Yes, they love the tradition. But if Ohio State's goal coming into the year is to play in the Rose Bowl, then their sadly undershooting.
So a playoff is the next step, right? I argue no. It just extends the same issues. There's subjective criteria, conference titles become secondary to defensible playoff position, you still have the same debates (i.e. this year, does 11-1 Boise make it ahead of 10-2 Arkansas?). And bowl ties are meaningless as they are now.
I'm here to say, the OLD system should be restored post haste. Tie the conferences to their bowl. Invite good unaffiliated teams as opponents. It would work out. Trust me. Here's the framework (bowl, champs):
Rose: Pac 10 vs. Big 10 period
Cotton: Big XII
Fiesta: All At large
Big East gets a berth but as an At Large or opponent. Assuming favorites tomorrow, this is how it would look this year:
Rose: Oregon vs. Wisconsin
Cotton: Oklahoma vs. Ohio State
Fiesta: Boise State vs. Stanford
Sugar: Auburn vs. TCU
Orange: Virginia Tech vs. Arkansas
Suddenly both the Sugar and Rose are in play. The Cotton is darn interesting, Fiesta ain't bad (on par with current non-BCS title bowls). Tradition is maintained and lots of debate.
Last year would look like:
Rose: Oregon vs. Ohio State
Cotton: Texas vs. TCU
Fiesta: Cincinnati vs. Florida
Sugar: Alabama vs. Boise State
Orange: Georgia Tech vs. Iowa
So you reshuffle two games, but makes two games of interest suddenly, the same quantity of teams will be undefeated, and if Texas and Alabama both win, perhaps split title, but bragging rights for the ages for sure.
What you sacrifice is the occasional 1997 scenario where Nebraska and Michigan are darn good but don't get to play. What you don't get is all or nothing that TCU has played the last two years, and Boise last year. All are still in the mix through the bowl games under this scenario. Admittedly, Texas vs. Alabama may not have happened. But in some ways, it didn't really happen as intended anyway with the Colt injury.
It's a trade off. Some years like 2005, things wouldn't have been as good without the BCS. But most years and overall, it gives all teams one goal...win the conference, go to YOUR bowl, win that, and see what happens.
I'd even entertain a "plus one" at that point. Go through the traditional bowls, take the two best winners by heritage rank and quality of opponent defeated, then "Let's get it on".