Given that tattoos and piercings are often an expression of bodily autonomy and self-expression, I don't find it too shocking that people who've experienced abuse (and often lack of those very things as part of it) would gravitate to it.
In the same way that anorexia is an expression of "bodily autonomy and self-expression"? Tattooing, piercing or cutting rather see to be forms of self-mutilation and self-punishment or chasing the short high of the pain in contrast to emotional numbness.