it doesn't work because the minors for football/basketball are currently set up for people after their NCAA farm days, those who failed to make the league. you take the top d1 talent and move that out to a minor league, all the 4/5 star HS recruits go to a minor league, that top talent develops and starts being the main pipeline to the NFL, people will start watching. it won't be overnight, but people aint gonna keep watching the leftover "scrub"/d-ii level talent in schools when all the best players are in a minor league that then feeds the major teams they care about.
as for school attachment, that's lie. most fans of these power schools never went to the school. it's a regional thing for some while others become fans during a certain era (90's miami, 00's USC) or for certain players. had the miami typhoons (minor league) fielded those 90's/very early 00's teams, they'd have the fans the U did/does.
again, yall are being shortsighted or thinking in terms of overnight success.
edit: and even if the public doesn't make it as popular on tv as the NCAA is now (which isn't just some shyt that happened organically in the first place), if the best talent is there, the leagues will know, and that's all that matters, especially if the NBA/NFL don't have to fund it - free farms are free farms. the only reason the NCAA is so strong is because it's a free farm and the NFL/NBA benefit from supporting their system.