They're very portable, so you can carry them around with you in case you come up with an idea of something to write on your Tesla while you're out and about. They stick to the surface quite well and don't wash off in the rain.
(Please try not to succumb to the temptation to write "F**k off Nazi Scum" or similar on somebody else's though like other people are suggesting. That might encourage people not to buy Teslas, which is a shame, because they're great American cars.)
But owning a car doesn't mean you agree with the ceo of the company on all matters...
I can't imagine anyone who purchased a cyber truck is unaware of what Musk is doing, so they are at least complicit in all of this. We aren't talking about vandalizing 8 year old model 3s, this is about people who purchased an 80+ thousand dollar hunk of sheet metal after Musk went full mask-off with his beliefs
The fact you think you're in the right for vandalizing people's property is delusional lol