Epic made tons of money on Fortnite and decided to spend some of them on an alternative to Steam; Epic Games Store. Even if it started out bareboned at launch, in 2022, it has a huge selection of titles, enhanced even further by plenty of exclusives and free games every week. There was also a lower fee for developers for each sold game, so the persons actually making the games made more money per sold Epic Games Store title than on Steam.
This, and the fact that Epic also bought companies like Psyonix (Rocket League) and Mediatonic (Fall Guys: Ultimate Knockout), has contributed to a rapid growth, and now they claim to have reached over 500 million users. While a whole lot of these likely are people only playing Fortnite and Rocket League or downloading free games, it is still a sign that Epic Games Store is a very busy platform going nowhere.
Thanks The Verge