Because of their huge fan-bases - national fan-bases in both cases. They move the media needle, even if they haven't won national championships lately. Notre Dame does the same thing but few people question why. Texas in particular is a national brand, as their apparel sales will attest.
Norte Dame finished in the top two of most viewed games last season. The big twelve did not even make the top ten. This may be one factor that is driving Texas and Oklahoma to the SEC and the SEC having an interest in those two schools. This data below is for the regular season.
TOP 10 MOST-WATCHED COLLEGE FOOTBALL GAMES (2020)
1. Nov. 7: Clemson vs. Notre Dame (NBC): 10.1 million
2. Dec. 19: Notre Dame vs. Clemson (ABC): 9.9 million
3. Oct. 17: Georgia vs. Alabama (CBS): 9.6 million
4. Dec. 19: Alabama vs. Florida (CBS): 8.9 million
5. Dec. 19: Ohio State vs. Northwestern (FOX): 8.0 million
6. Nov. 28: Alabama vs. Auburn (CBS): 6.7 million
7. Oct. 31: Ohio State vs. Penn State (ABC): 6.5 million
8. Nov. 7: Florida vs. Georgia (CBS): 6.3 million
9. Oct. 24: Nebraska vs. Ohio State (FOX): 6.2 million
10. Nov. 21: Indiana vs. Ohio State (FOX): 6.1 million
TOP 10 MOST-WATCHED COLLEGE FOOTBALL GAMES (2019)
1. Nov. 9: LSU vs. Alabama (CBS): 16.6 million
2. Dec. 7: LSU vs. Georgia (CBS): 13.7 million
3. Dec. 7: Ohio State vs. Wisconsin (FOX): 13.6 million
4. Nov. 30: Ohio State vs. Michigan (FOX): 12.4 million
5. Nov. 30: Alabama vs. Auburn (CBS): 11.4 million
6. Nov. 23: Penn State vs. Ohio State (FOX): 9.4 million
7. Sept. 21: Notre Dame vs. Georgia (CBS): 9.3 million
8. Dec. 7: Oklahoma vs. Baylor (ESPN): 8.7 million
9. Sept. 9: LSU vs. Texas (ABC): 8.6 million
10: Oct. 12: Oklahoma vs. Texas (FOX): 7.3 million