Was interviewed in this article that talks about why people buy things in the game Fortnite:

https://morningconsult.com/2018/05/10/fortnite-battle-royale-success-signals-mobile-gamings-future/

For “Fortnite: Battle Royale” players, these in-app purchases are just cosmetic: “skins” that change one’s appearance or “emotes” that allow avatars to dance, for example.

“These are things that are not necessarily tied to the mechanics of the game themselves but something that could be related to the player’s self-identity,” said D. Yvette Wohn, an assistant professor at the New Jersey Institute of Technology who specializes in human computer interaction and social technologies.

The currency in “Fortnite: Battle Royale” is called V-Bucks, and 1,000 V-Bucks cost $10. Skins and outfits cost about 800 to 1,500 V-Bucks, and emotes are about 200.

“Especially if you’re spending a lot of time in the game, your character in the game becomes a part of your identity,” Wohn said in an interview May 2. “So why wouldn’t you want to spend money on clothes? Because that’s what you do offline, as well.”