Random googling turns up 87 colleges that have residency requirements[1]. So you're right that it isn't "most" but it is also not super rare. I'm just saying its a sneaky way for colleges to bump up costs. Most college students won't go through the work to get a waiver and will just go with the flow. Its like the difference between opt-in and opt-out.
https://www.washingtonpost.com/local/education/freshman-resi...