The answer to this question is a little bit complicated. There are actually two types of funding in Fortnite: game funds and player funds.
Game funds come from the game's developers, Epic Games. They use these funds to pay for things like servers, support, and marketing. Player funds come from people who buy things in the game, such as V-Bucks (the in-game currency) or cosmetic items.
Epic Games does not release detailed information about how much money they make from players, but we do know that they made over $1 billion dollars in 2018 alone! This means that there is a lot of money flowing into Fortnite, and it's only going to continue growing.
We also know that Epic Games reinvests a lot of this money back into the game. They've used player funds to add new features, improve existing ones, and even create entirely new games! For example, they recently released Battle Breakers (a mobile game) and Shadow Complex Remastered (a remastered version of an older PC game).
It's clear that Epic Games is committed to making Fortnite the best it can be. With such a large amount of funding coming in, there's no doubt that they'll be able to continue delivering on their promises for years to come.