One could also point out -- as a secondary or tertiary driving force -- that most Nike athletic department contracts these days are written to include some ratio of cash to Nike equipment. That means the schools don't get their stuff for free. They either use part of their "stuff allotment" to order it, or they pay for it (because they don't have an allotment or have gone over). So this means that even in the theoretical world where literally zero fans buy a new alternate jersey, at least ~300 of them will be sold, if you assume that each Big Ten team will order its game jerseys in triplicate. Which is at least a guaranteed $30,000 in revenue.
That's extra revenue that can only come from new products and, again, comes with massive profit margins. And all of this is without insisting that at least 100-1000 fans are buying any jersey Nike puts out, no matter how ugly. Seriously. I think it's true: Literally no jersey can monetarily fail for Nike. Even the ones that you never see on the back of a fan.