Without spending too much time on current events, it's worth making a cursory statement that the demographics and nature of American colleges don't typically reflect what's seen in the movies. Which is to say, there is a large portion of college students who are very much "get in, get your degree, and get out" and many students go to college in their own state. NCES offers a collection of statistics related to college students that provides a bunch of context around who it is that attends American schools. Our friends at /r/AskSocialScience may be able to speak more to that.

That said, you asked at Ask Historians and I would be delighted to offer the historical context. First things first: the American dream and the idea that America is, in theory, a meritocracy. This sentiment shaped the evolution of the K-12 system in both passive and active ways resulting in a structure where the K-12 system offers students a liberal arts curriculum for all thirteen years. Unlike, for example, German teenagers, American students at the secondary level are not tracked into different paths related to future career options. Students can choose different tracks such as vocational training but that's entirely up to the student and their grown-ups. In other words, there is no structure in American public education for explicitly preparing children for the workforce. Instead, schools have guidance and career counselors to help students make choices about their life after high school. (No, schools aren't about preparing factory workers. Yes, "American public education" is a bit of a misnomer. Yes, there's a relationship between K-12 education and why 18 is seen as the beginning of adulthood.)

What this means for young people is that the time to prepare for a career happens after secondary school - which is to say, college, university, community colleges, or trade schools. In his 2014 history of American higher education, Geiger describes the history of American higher education as being a history of, "culture, careers, and knowledge." Each of these constructs created and maintain feedback loops between American society and colleges and universities.

The workforce feedback loop has existed since the beginning: someone (typically a politician or philanthropist) identifies a need and establishes a school to prepare people to meet that particular need. Harvard came about because (basically), in the late-1600s, there was a need to prepare more New England boys and men for the ministry. Dozens of normal colleges, or teacher preparation schools, were founded during the common school movement in the 1800s because teachers needed more than a grammar school education. There was an explosion in trade, business, and secretarial schools in the early 1900s as high school became routine and employers determined a high school diploma alone was no longer sufficient evidence for preparation for the workforce. Additionally, many of the colleges and universities founded as a result of the Morrill Land-Grant Acts in the 1800s were about preparing students for industrial trades. What this means for your question is that some colleges have a reputation for preparing students for very particular careers. As an example, Berklee College in Boston was founded explicitly to focus on contemporary music creation and production. If a young person wants to study forestry, they're likely to head to SUNY College of Environmental Science and Forestry in Syracuse, NY. These types of idiosyncratic programs advertise across the country and when you bring groups of people together, they create a culture of their own AKA "college life."

The second feedback loop is knowledge. Harvard expanded its courses in the early 1700s, establishing what is thought of as the "classical curriculum." Students studied Latin, Greek, some maths, some sciences, rhetoric and logic, and possibly religion. In effect, they left Harvard knowing the things that smart men knew and went off and did what smart men did - business, politics, law, preaching, etc. Kings College (now Columbia) was founded, in effect, because the men in or with access to power in NYC didn't want to send their sons to Boston. They recognized they could provide their sons with the knowledge base smart men had without sending them far away and having them miss out on network opportunities (that's the third feedback loop.) As states established formal, tax-payer funded K-12 systems, they began to play a more active role in creating places for residents of their state to gain knowledge. The "SUNY" from the previous paragraph refers to the State University of New York, a system of colleges, universities, and community colleges across the state. Some of the schools in the system were founded to serve a particular career purpose (Shout out to Fredonia College, AKA SUNY Fredonia, originally New York State Normal School), some were founded because there was no college in the region of the state. Other states created similar systems, including the California State University system. Many of these schools were founded to be liberal arts colleges - meaning a young person would gain richer and deeper knowledge than they gained in K-12 with the thinking that a richer knowledge base and the skills developed in college would prepare them for most careers.

This leads us to the third, and likely most relevant to your question, feedback loop: culture. While Harvard was founded as a school for preparing men for the pulpit, it quickly became a place for networking and making or strengthening, social connections. While they were there, the students - all young white men - formed friendships and relationships that would go on to shape the rest of their lives, and the country itself. The men who founded other Colonial Colleges often saw them as a way for their sons to network and connect. Yet, despite the insistence that America is a meritocracy, the history of higher education is deeply linked to hard and soft segregation, institutional sexism, racism, and ableism. As such, many of the colleges founded to prepare young people for particular careers or to offer a richer and deeper knowledge base purposefully excluded a whole bunch of the college-age population. The Seven Sisters (more on them here) were founded because the Colonial Colleges refused to admit women (and some women didn't want to learn with men.) Historically Black Colleges and Universities, as well as Tribal Colleges, were established because Black and Indigenous students were barred from Primarily White Institutions (PWI's.) Gallaudet University and NTID were founded because deaf and hard of hearing students were barred from most colleges and universities. (It's worth noting that the exclusion doesn't always go both ways. While most cis-women-only colleges have begun accepting men and trans women, HBCUs have always accepted students of all races and ethnicities.)

A natural consequence of having colleges created for members of a particular community is they develop their own culture and norms. For young Deaf adults who grew up with hearing parents, being at Galludet was their first opportunity to be one of many, as opposed to an outsider. One can imagine the sense of community and freedom that came with being a young Black woman at an HBCU, founded by Black women and men for the purpose of giving you a rich and broad education. We see this idea - that creating a community with a strong sense of belonging and connection - in the rise of fraternities and sororities in American colleges. (The Company He Keeps by Syrett is a good look at the history of white college fraternities, which is a different history than Black college fraternities, which is a different history than Black college sororities.) Meanwhile, some students attended colleges ONLY for the purposes of networking. It's likely that the best-known example of this is the phenomenon of young, high-class women attending co-education colleges with the goal of getting their "Mrs." degree. While it's likely it didn't happen as often as is mentioned in period TV shows and movies, it did happen enough that it's mentioned in wedding announcements of the era.

There's one more feedback loop worth mentioning and that's the expectation young people have about college. While, again, I have to defer to social scientists about current events, we see a mental model of what college is "supposed" to look like - dorms, parties, etc. - forming in the 1950s and 1960s. The concept of a "teenager" and "teenage culture" was now the norm. The ranks of college students exploded as a result of the GI bill and increased funding at the state and national levels. The rise of college football as a sport and economy shaped how students saw their relationship to their school. Schools began to require SAT scores for admission, meaning they could offer metrics about their student population, creating the idea of "good" colleges versus "fall-back." Parents would advocate their children go to the same college they went to (known as "legacies"), meaning their child had an expectation of what college would look like and would, knowingly or not, seek to fulfill those expectations.

So, in other words, young people receiving a tertiary education in America have been raised to see college as an "experience" and as such, make the four (or five or six or seven) years between high school and "real life" something different and special from the rest of life.