It is difficult to claim "We're determining the national champ" when Indiana is on the field... or SMU or Clemson or Arizona State. None of those teams is deserving of an opportunity. So credibility is lost immediately.
What happened was that the major conferences looked at the economics and came up with something that addressed all of their monetary desires. We want to protect the conference championship games. We want guaranteed money for as many of the major conference teams as we can get. They left out the previous requirement "We want each team to have a legitimate argument that they are the best team."
And once you do that, you easily can expand the tournament to include a lot more teams - that is the obvious plan.