Why does the average person go to uni nowadays? Because most well paying jobs nowadays require that magical 2:1 degree, in anything. Because in many parts of the UK it's the only way to get a decent job.
Many will say "to doss around for three years and drink heavily" but I don't think that's the case. I certainly think it's an added bonus of getting that magical piece of paper, but I don't think it's the sole reason. Many people from my school went into apprenticeships for oil & gas firms. They earn a hell of a lot of money - more than most people with degrees will ever get - and thus didn't see the need to go to university. The four years (we're talking about Scotland here) of drinking and lie ins didn't appeal to them as much as high salaries and on the job training, learning only things that are directly required for work.
And let us not forget that you don't have to go to university to have fun. I'm one of the only folks from my high school class to go to university and when I used to return home it certainly wasn't the case that I was the only one who knew how to have fun! If anything it was the opposite because I have a very high workload in my degree and it's common for me to have to work well into the night, whereas they were done at work at 4-5pm, and had enough money to run decent cars, wear decent clothes and not have to drink cheap vodka. Uni has the advantage of being away from home - and I've done things my straight-to-work friends will never do - but it's certainly not a prerequisite to having a good time as a teenager. It hampered mine, although this probably doesn't apply to those doing courses with only 3 contact hours per week...