Friends from high school change. Living off campus with friends makes an unsaid pact to stay with each other no matter what. This doesn't work, and in the end, the apartment may become a feeding ground for fights. Leaving the apartment is an option, but leaving costs money. Living on campus maximizes those pennies.
Most college campuses come furnished, prices including utilities, TV and even the Internet.
When moving away from home, new adults have to buy everything. Most don't have towels, dishes or even a broom. Now add to those expenses a bed, dresser, refrigerator, utilities, cable, and rent. Plus gas for a car, food for the refrigerator, and sheets for the bed. Don't forget tuition, books and school supplies.