I see you got some downvotes, but no really this is true. Diversity is a frequent selling point, and you get a chance to meet people from around the world at university. Clubs, sports, frats, job networking, are all socially driven. Some people need the social feedback to drive their studies; we're social animals so there's really no shame in that.
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.