I haven't been in university in over 20 years, but when I was, I absolutely did not have hundreds of dollars to throw around for things to make my life more convenient. Certainly some of my peers did, but they were not in the majority.
Convenience was not a factor. If you were unable to sign up for some of these courses, you would be barred from advancing in your studies. These were things like prerequisites for applying to your major, not just shuffling around your timeslots for an ideal schedule.
Im unsure if this was much more of an issue at UW specifically (also this was also over a decade ago), but UW accepted maybe ~30% of the applicants to a given major (in STEM). They dont tell you this as a freshman when you declare your intended course of study, but you're competing with your classmates to actually be able to study what you want to major in. This leads to critical classes filling up within seconds, massive waitlists, and delays of semesters possible if you miss courses you need.