My Alma-mater gave me access to leaders, hiring and referral opportunities, and even a life long partner with similar ambitions. I can probably name a good long list of of people I can call and get a a little help from now if I was in a bit of a pinch or need a little perspective.
Granted, I went to a smallish regional state school. The experience there, or at, say, Small Liberal Arts College, may be very different from Big State Engineering or Pressure Cooker Elite U.
Sometimes though, we need instruments to do science, so that's another major purpose for undergrad work. Occasionally. But if the undergrads decided to all take online courses one day, it would sure help the grad get work done.
Probably? Personally my first semester at uni was depressingly dull other than the novelty and the subjects (well, mostly dull there too but the future semesters looked interesting and I was programming for the first time). By chance I was walking through a club recruitment event when a single person stopped to talk to me and tried to convince me to join and come to a meeting that night. They got my email too. Well, I didn't go to the meeting but a few days later an email showed up saying the first practice will be tomorrow. I figured why not, I'm not doing anything, and showed up. I stuck with it for four years, taking on duties over time until I was president, it was most of my social life (e.g parties, hanging out) and I made most of my friends through it, shifted my lifestyle from videogames and procrastination to working out, having fun with sport and mastering it, having flow/mushin consistently, and getting work done ASAP, and other considerations.
I've never felt the desire to donate to my old college, but certainly I already have donated to my old club and have considered doing more for it. I assume folks with very good experiences were part of some sort of organization: my high school friends that stuck together in college without branching out had a good time but was overall meh.
Sorry to hear that. What are some ways to cheat school? (waste of time)
Edit: apart from catching on your reading (listening) and scrolling on hackernews.