Tattoos are part of tribalism, tattoos are about fitting in but to the unaware they think they are new or original, it's about being cool.
It is to signal to the world you are something.
You will tend to find that people like them flock together, they find their people.
The most intelligent see above trends, tattoo's are just trendy like clothes and change over time.
Humans have a need for people, not all people have this need rampantly so out of control.
There is also the factor that we as humans do things in symbols (Symbolism) so we can tell great stories with just 1 symbol or tattoo too.