Epic is an actual studio, and they have more than enough money to create additional games if they actually wanted to. Thing is, they clearly don't want to.
They actually had two other titles in development when Fortnite took off, but instead of using the money from that game to improve them and get them out faster, they just axed them. All they have done since is take games away from other platforms.
Yeah, they own Rocket League now, and I guess in a way they're "maintaining" it. But that game was already incredibly successful. It was being maintained just fine, and the developer wasn't hurting for money. The buyout had zero upsides for the players, all it did was force those playing on other platforms to install EGS.
Do you not realize that they're not doing that shit for you?
They're pimping out the game as an ad platform.