It all comes down to supply and demand, as @gpo613 says. If you’re in a large state with a lot of student applicants there’s going to be ample supply and the state isn’t going to make a ton of effort to lure in outsiders. If you’re in a low population state, or one with bad secondary schools, then there might not be a decent supply of good students so buying some top test scores might be a good investment. In a smaller university it doesn’t take that many to move the needle a little, which is why MS and AL and UT and SD and OK and a bunch of others are all throwing around pretty good money to bring in excellent students and hopefully make them residents.