Just like that song goes, people pay their surgeons very well to break the spell of aging.
Everyone is obsessed with staying/being young these days.
It doesn't matter how you look at it – there are so many things that lead to this genre's popularity, it's impossible to imagine it getting irrelevant or losing the top spot.
Many people deem this obsession with young girls "creepy", but who cares about those holier-than-thou types?
There's no ifs and buts about it, people have always enjoyed pornography. So, to make a long story slightly shorter: we love porn. Almost everyone is sex-obsessed it to the nth degree.
There are also people who tend to easily forgive and overlook unenthusiastic babes who just starfish it up as long as they are young and beautiful.
Everyone is into something freaky, and this genre is as vanilla as they come. This one is truly amazing, because who doesn't look back fondly on the years spent in college?
If you're not into something freaky, then shame on you – what is there to your boring, mediocre life? Anyways, this brief piece is turning into a filibuster-looking wall of text, so let's focus on the most popular genres when it comes to beautiful/energetic/sexy young people fucking in front of a working camera. You might end up rewording this whole thing slightly, and BOOM – you have an actual paper/thesis on pornography. You don't like your student loans, sure; but you did love the whole freedom thing.
There's a huge demand for taboo step-family pornography, for example.
You get some young minx and her middle-aged looking bald-headed step-brother, supposedly the same age.