You are saying that the “Popular Schools” should only be in the tournament which is straight up wrong. If that were the case, no one would care. It would be the same thing over and over again. The March Madness would die down and no longer become a national sensation and just turn into the CFB Playoff.
There are a lot of schools that plays their hearts out to become the best team possible in the nation by that season and give their all to make the NCAA Tournament. And the best part about it is that they always prove the naysayers wrong with unexpected runs.
Sure, top teams always win which is always expected, but you never know who can make an impact in the whole thing. Princeton, St Peters, FAU, etc. are examples of teams that get into the tournament either by auto qualification or at large bids that make games those like they are the last game of their season or for some, their college careers. They want to play until they cant no more regardless if some don't make it to the first round or fight and win all the way to the 2nd round, sweet 16, elite 8, final four, or even the final game.
People come into the NCAA to play and to win and putting the big schools into the NCAA tournament would waste their chances. CFP is poor because they care about revenue and only care about the 4 best teams (extended to 12, but they need autoqualifiers (if they do, correct me)).
And also, its mainly the P6 since the Big East is a major basketball conference. They and some other conferences that made an impact like G5, developing conferences like WCC, and smaller conferences can go out and represent their team and their conference in the NCAA
(Also the message above was accidentally sent because I did not mean to hit send from my mobile device, so i had to write another (basically it happened when i started typing))