This is a good question.
Maybe it becomes a status symbol? I think that explains the tattooing, in some cases. "OH you have them on your neck? Well look a this - I'm gonna do all over my bald head and I might do my face next if my wife lets me!"
It's a lot like owning trucks. Who has the biggest damn truck? I think tattoos are that way for some men - insecurity and a need for attention on display.
But for other people, tattoos really are art. They are artistic and they think they are pretty/cool.
But, why do fads get stupid?
A. People are making money off of them.
B. Fear of missing out or being uncool.
C. Advertising. OMG, you have no idea how much advertising is LASER FOCUSED on teens and pre-teens. Not thru TV like in the old days - now the ads are coming through whatever Internet they use. Then they grow up and the same amount is focused on college students; then they graduate and the same amount is telling them to buy tons of stuff for their first apartment. They they get into their 30s and they are targeted with ads for every baby and child item you can imagine - strollers that sell for $500 and up, etc., etc.
Do you know why they don't target Seniors with so many ads (expect for loans, Medicare and meds)? Because studies have shown that by about age 50ish, consumers are SET IN OUR WAYS. We know which brands we like and we stick with them. We are not so easily swayed by advertising as the young, so they don't waste any ad dollars on us except in very limited realms.