Why do nonresidential students have to pay more?

Non-residential students at colleges and universities pay more than residential students primarily because they don't pay for on-campus housing and often some meal plans. The cost of tuition itself usually remains the same (or very similar), but the overall cost of attendance is higher for residential students because of these added fees. Essentially, the university is covering the costs associated with providing housing and food for residential students, and that cost is included in their overall fees. Non-residential students don't receive those services, so they don't pay for them.