A good portion of why the tattoo exists is to be ugly.
In military terms, it’s to intimidate others and share an intimidating image with others. Because let’s face it, if you need a permanent marking on your body to remember something, your memory is worse than mine, and I border on Alzheimers.
In non-military terms, once again it’s an ugly thing to signal to others that you are a badass (whether you are or not, doesn’t matter), or to signal to others that you are open to strangers touching your naked flesh to do visibly nasty things to it.
It’s become a fashion thing since 10 years ago, but that’s mainly because they’re a lot easier to remove than before. Not that they’re easy really, but (thanks to lasers) relatively easier with better results than before.