Tim Sweeney's idea of item ownership persisting across games would imply people pay only once, which is a good thing. It's not exactly a novel concept because Valve and others have done it for a while, but what's new is Epic making it easier for Unreal Engine developers to incorporate those same assets into their games, as opposed to having to create them from scratch.
I don't know about other games, but Fortnite doesn't sell mere JPEGs or reskins. The different styles offered for an item are included in the base package. The models and their textures cost developer work hours, so they need to be paid, but Epic also essentially gives away its battle pass for free because after a few seasons of playing, you can have enough vbucks to pay for the premium path and get those vbucks back. That's multiple outfits, emotes and other items.
And lastly, IP collabs are fun. They're the reason people like me would check out a game I otherwise wouldn't. And making the likes of RoboCop dance is great!