Pre-drinks being drinks at a friends house. Sit around having cheap drinks bought at the bottle shop. Then head out to the bar/club and either dont drink or nurse a beer or 2 over the rest of the night. Pre-drinks were usually the most fun part of the evening anyway.
Long before 21, genuine serendipity and mutual interest fall away and cynical "networking" takes over. I'd say the transition happens, on average, around sophomore year. Once people get their first experiences with the working world, they realize how much social class really matters and will do everything they can not to lose ground in the shuffle.
The higher (or lower, since it's the middle class that has the longest period of class naivete) you go in social class, the earlier this transition happens. It's why you don't actually as many connections, if you don't come from wealth, at an elite college as people think you do. The legacy mediocrities (e.g., final club brats) and the middle-class smart kids who actually earned their way in don't mix. If you're going to make connections in the US, you have to do so before class/caste identity really hardens and they learn to see you as an enemy; that's in prep school.
There are class differences and some level of class separation everywhere. It isn't a distinctly or even more more pronounced American trait. As for class differences in college my experience was that I made and have had enduring friendships with people from all different social classes that I made in college. Some of my friends from college came from extremely wealthy families, made for some great mostly free for me spring break trips, and some were working multiple jobs to get through school. Those working the multiple jobs and those from wealth were also friends. Are some wealthy people snobs and jerks? Yes, but I have also met just as many reverse-snobs and jerks. My experience is being a jerk is a distinct trait with no direct connection to your social class. I'm mentioning this only because you say elite college in your comment and I don't want to have someone say the experience is different for elite colleges. I went to a university which is consistently ranked by those publications which rank such things as being in the top 10 and in specific areas of study in the top 3 programs in the country.
As for the original premise of whether college is needed to make life long friendships, I actually don't agree. I have life long friends from before, during and after college.
Eventually, people realize they were cattle being raised for slaughter, and that "the corporate ladder" isn't going to lead anywhere decent for them because they weren't born into the right connections for that, but by this time they've had all their energies wrung out of them and it seems to be too late.
Folks counter this by pre-drinking at home and then going home to continue drinking. It really wouldn't be that difficult in the US either, and some folks would certainly leave you behind if you can't keep up financially.
Fun fact: Austria is cheap in comparison, at about 2,50€ to 3,50€ per beer, and it seems like a comparative deal. [2]
[1]https://norwaytoday.info/travel/is-beer-in-norway-really-tha.... [2]https://www.flatio.com/blog/typical-prices-of-goods-in-austr....
The UK also heavily taxes alcohol but you'll find cheap beers (sure, some London pubs will still charge you 5£ or more for some beers).
Even the latter reduces hard core binge drinking and the former really seems to help with the rampant alcoholism in winter at high latitudes. Paternalistic, but that is the price of living in a society (with free healthcare systems and A&E that get overtaxed by drunks…)
This describes me (well, 3 years at CC, but close.) However, I also managed to find the nerds by getting a low-level job at the state school's computing services center, and they're still my friends 30+ years later.
My read is that there are a lot of confounding variables here, but I'm inclined to think that college tends to makes it easier to build a friend network of upwardly mobile people (in the US in the last four+ decades.)
That's quite a number of college attendees (graduates?) standing on the shoulders of a single personal anecdote.
I'd estimate an equal number received prank phone calls their Freshman year from inebriated idiots fascinated by the length of their Sri Lankan roomate's name as it appeared in the student directory. (Yes, a physical fucking student directory!)
I went to college and lived there. I was far enough away from home that I could not return home with any frequency. I was a nerd at a college full of nerds and other like-minded people. I intentionally put more effort into making friends by participating in various clubs, social groups, and activities. I put more effort into that than I did into my studies. I did just enough schoolwork to graduate. Indeed, I did form lifelong friends during this time.
Now compare that to the story of another person I know. They went to community college while still living at home. After a year or two of that, they did leave home to go to college. However, they were at a state school with people studying various things and having various interests. There was not a group of like-minded people there. Lots of the students there were commuters and not living in dorms. This person focused on their studies, not on socializing. This person's social group today is largely still comprised of their friends from high school.
This scenario that OP describes happened for me, and presumably for OP as well. It doesn't happen for all, or even most, people attending college. It only happens for the right people who attend the right college in exactly the right circumstances.