If Fortnite was so profitable, then why has Epic gone into the digital storefront business? Even they know that their biggest cash cow will run dry at some point. If they don't change direction of the company now, it will have been
too-little, too-late.
Epic is in the process of diversifying itself right now much like Valve did. Have you noticed that Valve haven't put in any major resources into a big new title and yet Steam ramped up the new features over the past few years? Epic is a company that facets all business of video games with the exception of selling them until recently. They collect licensing costs for their Unreal Engine, they develop their own games in-house, and now they are to sell them.
I'm not saying that the way that they are handling themselves is right, but a wise business move is to diversify before you're strapped for cash. All it takes is one purchase to lock you in to their ecosystem... and they're trying to tempt you.