They've already done the political convention. They've done NCAA tournament games. A one off brings exposure for about 2 seconds and then the stadium sits there for 40 years as people go Cleveland, why go there when LA, New Orleans, Tampa/Miami, Dallas etc can host. They'll go back to NY before they'd do Cleveland. They need a flashy city to host the biggest event of the year, again the SB is more than the game, that ain't Cleveland.
Why don't I see Buffalo fans going hey we could get a SB? NE fans, Pittsburgh fans, Denver fans Green Bay fans etc. 90% of people couldn't afford to go anyway, I can watch the game on TV from LA just as easily as Cleveland.