It's probably someone who is really into productivity and self-improvement, makes it part of their identity, mentions it to their family... and then has 10 pairs gifted every xmas.
That seems like a less bad version of handing out specific items of company swag ("woo, a t-shirt in the wrong size"). At least you can pick something that's useful to you.
We get a certain amount of money a year to buy GitHub swag, but in fairness, I think our shirts and swag is pretty great and most employees appreciate it/use it.