There is a simple matter of investment. Shoe companies sponsor universities.
"The lucrative link between shoe and apparel companies and universities is a matter of public knowledge. Adidas' deal with Louisville is the company's second-largest with a university, behind only Kansas.
Portland Business Journal's
database shows deals between public universities and apparel companies, including Nike, Under Armour and Adidas. Private schools are not included in the database.
These are the six largest college shoe and apparel deals, via ESPN's Darren Rovell:
UCLA & Under Armour: 15 years, $280 million
Ohio State & Nike: 15 years, $252 million
Texas & Nike: 15 years, $250 million
Kansas & Adidas: 14 years, $191 million
Michigan & Nike: 15 years, $173.8 million
Louisville & Adidas: 10 years, $160 million"
To protect this investment, the shoe companies need to make a return. This return is through shoe and apparel sales, among other miscellaneous streams. In order to market their brand they need winning products on the floor (why do you think the P5 teams get the biggest contracts?) and there lies the incentive to push players to the schools with the greatest investment.
It is that simple.