A few things go into this

1. being able to have nearly anything you want on a whim increases the perceived value of the things you can't just automatically have the moment you want it.

2. it's mostly attractive successful guys because they can have any woman they want. It's much harder for an adult man to get close to a 15 year old than it is for them to get close to a 25 year old.

3. For a huge variety of reasons 14~18 is what evolutionary pressures from humanity's hunter-gatherer origins have led to being "peak reproductive desirability" for human females, and it's only in the last 100 years or so that european social-mores have stopped seeing people as adults by 15~16 and started seeing people as powerless children until 24~25

4. Hypergamy is the norm across all human cultures, nations, and races, and it turns out teenagers have similar tastes and behaviors to 20-somethings