system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: The significance/obsession of USA citizens with prom and high school graduation.

Is there something that I'm missing here? 

I thought it's normal to finish high school and prepare to go to pre U than Uni. 

But after seeing limousine being rented, hundred plus USD dress, another hundred plus USD for shoes, and top that with another couple of hundred USD for other necessary stuff, I'm questioning my own logic. 

It doesn't stop there, it seems, graduating high school is widely celebrated even to a point that parents give out paid vacation trips or a car as gift. 

As for the students theme self, OMG they spent months preparing for prom and the fight for Queen and King is actually real. I thought it was just TV shit. 

Back to the question, why? what is it I'm missing here?
gpt
TL;DR: We've lost most of our developmental milestones and coming-of-age rituals. So high school prom and graduation are a major milestone for most people, often the *only* milestone. They're an important cultural event and ritual that signals a transition from childhood to adulthood. People want to mark the occasion and remember it later in life.

The US, like many Western societies, is gradually secularizing. It is also highly urbanized. And finally the cultural importance of marriage and the nuclear family has been declining for decades. As such, we've found that many of our developmental rituals have faded away. 

In many religions, there's some type of coming-of-age ceremony. Jews have bar mitzvah at age 13. Many Christians have Confirmation around the same age, where children are taught important theological points and are allowed to take communion at church for the first time. Lots of cultures have various rituals and ceremonies for the time when a child is perceived to have become mature and able to take on adult responsibilities and privileges. These ceremonies aren't always religious, but in America, historically, they have been. Most people in America, even if not personally religious, have a Christian background. But religion has faded greatly from public life. Most people rarely go to church, if at all, and a sixth of the US population has no religion. So religious coming-of-age ceremonies are gone for many people.

Second, we have urbanization. Rural areas tend to be "old-fashioned." Traditions are stronger. There's a variety of reasons for this. Part of is it the closeness of communities. In urban settings, you can be alone, you can get lost. If you have no interest in keeping up traditions, there's no local authorities: familial, religious, or economic, to force you to keep up with tradition. If you stop going to church, stop wearing traditional clothes, stop going to holiday gatherings and other ceremonies, no one's going to notice. But in rural settings, people rely heavily on one another, and you'll be gossiped about heavily if you're an oddball who doesn't keep up with tradition like everyone else. So you do. Rural areas often have all kinds of gatherings and rituals, especially for children. Barn-raisings, harvest festivals, Christenings for babies, and especially early marriage. In old times, in rural places, people often moved straight from their parents' house straight into a new home with their spouse. They married at 19 or 20 and started having kids immediately. Weddings then became a huge deal. You kindof weren't an adult until you got married, but there were always the occasional "bachelors" and "spinsters" who delayed marriage or never married. This has gone away. The average age when a woman first gives birth now is 27, compared to 22 a century ago. And marriage is delayed as well. We now give weird looks to people who marry before 21. That used to be about the average age people got married. Now it's not abnormal to wait until you're in your 30s to marry and have kids.