Bookstore a center of campus

[decadence]

Another thing I'm wondering about, bookstores on a US campus are a central part and don't sell just books. On a campus there might be a store for snacks, food and magazines, maybe a small greek store etc etc.
But school merchandise, t-shirts, sweatshirts of whatever always seem to be sold in the bookstore. WHY there and not the convenience store which sells snacks, frozen foods etc. Clothing and stuff seems always sold in bookstores.

Oh and also are the bookstores ever external company branches (like a Barnes & Noble or Borders) or just RCU bookstore? (R for Random).

edited for spelling