SEC hate is the only real answer.
The rest of the nation were already jealous of the prestige, tradition, passion, and money of the SEC. Their anger reached a high point under the BCS run the SEC had, particularly when Bama played LSU for the title.
So they invented a 4 team playoff system. And they were absolutely happy with the Playoff when it yielded Ohio State versus Oregon for the Championship...they did not complain or call for the Playoff to be expanded because it had seemed to achieve their intended goal of stopping the SEC from winning College Football Championships.
But now the SEC has 2 teams in the Playoff Championship Game and they are unhappy again. And they are calling for an expanded Playoff or any number of different new rules that should be made to the Playoff system now.
"Conference Champions Only", "Strength of Schedule", "Should have to play NINE Conference Games", "Eye Test", blah, blah, blah, la, la, la, da, da, da. I don't care which stated narrative they use...the clear unstated motive / force driving their talking points is "We are tired of the SEC, God I wish we could keep the SEC out of the Playoffs".