This is how Musk does marketing.
He takes a random item, orders a few thousand, slaps one of his company logos on it, and charges 10x what it cost.
It generates some buzz for a few hours and drives traffic to Tesla's website which is the primary objective. And it also generates a small bit of profit. In contrast to most marketing which costs money instead.
In the past he's sold flamethrowers, backpacks, belt buckles, tequila, whistles, perfume, power wheel cars... there's probably a few other random items he's sold that I'm blanking on right now. Inevitably they sell out because the point was never actually selling them. I suspect he just bulk buys whatever random item was overstocked.