You likely don't know the entire story (understandable as it was four decades ago).
Unlike most cases where there was an attempt at plausible deniability and while many within the school with a wink and a nod attempted to give the appearance that they didn't know kids were getting paid or who was paying them, SMU had regular "board meetings" with the board being the school's president, a couple other high level school officials (including members of the athletic department) and some high powered boosters (who sourced the money). The meetings were designed to improve the effectiveness of recruiting players to be able to compete with the best teams in the country.
Part of what blew up in SMU's face was that the president, while running for some elected office (I think governor but it may have been senator) in a TV interview (not long before the death penalty) claimed (as there had been recent sanctions) that he had no knowledge of booster payments, only to be shown a letter to a player, with his stationary (as SMU's president) and signature thanking the kid for choosing SMU and including a copy of the check that was enclosed in the letter.
That is what led the NCAA to take steps that they never felt they would have to take.