When it's from a highly skilled artist, it's like wearing a painting. You're making a permanent blood commitment to art. Sure that's a dozen hours of mostly annoying pain, but then every time I look in the mirror my legs are just boring flesh. My arms get to be my favourite things in my favourite artistic style reminding me of the time I spend in my favourite place. It's a constant connection to those things that I can't accidentally wash off. A custom temporary tattoo version of that would probably be more expensive over time, more annoying to put on, and I wouldn't want to wear other sleeves or have have uneven/full body ones.