[rubiety]

Room and board is double-counting. You'd ultimately have to pay for that anyways (college or not), so it's hard to attribute that entirely to the "cost of college" - it's not a net cost.

[rayiner]

Counting tuition + room + board + opportunity cost is double counting. But you have to count either room and board or opportunity cost.

[dredmorbius]

It still needs to be paid and financed. Many colleges are in higher-rent areas (though many also are not). Students will need loans, income, stipends, or grants for these expenses.

Books are another large cost.