Why? Because it "looks good"?
Have you seen them when there is no backlight on them?
Absolutely dreadful - like you've been burned or scarred.
Some UV ink contains phosphorous, carcinogens, and allergens and you risk your body rejecting the tattoo. There has been a statistically higher number of reactions and complications with the UV tattoos than with regular tattoos.
If you're gonna have a tattoo, have a real nice regular one rather than something thats just "fashionable" that could cause you no end of problems.