Because the NCAA allows it and monitors the gifts. They are only allowed to give so much of a dollar amount to each athlete.
http://www.ncaa.org/...tes+can+receive
Not only that, but I think the ncaa monitors gifts given to the players from their schools during the year and counts that against what they can get from the bowls. Like those gold pants the Ohio State players got have a monetary value and that counts against their bowl swag... or something like that.
From the link it's sounds more like the institution can give an annual gift, that is separate from the bowl package. But the bowl package can have gifts from the institution and the bowl committee that both count towards the post season award, so together they couldn't exceed the limit.
Funny how ncaa rules could be confusing. This group can give this gift and that group can give that gift, but only so much and no more and if you trade your gift for tattoos you're the worst person ever and there has to be a big investigation. But it's all a gift, and you're still an amateur, thousands of dollars later.