Just a small correction: I don't think anyone pays for UE nowadays. Epic used to charge a monthly fee, but they've done away with that. Now you only pay royalties if your game is commercially successful. Which is different from paying for the engine itself.
Additionally, they mention that you can still negotiate paying an out right fee to license the engine if you'd like to do that rather than pay royalties (though I suspect it's mostly AAA studios that are interested in this)
It's for AAA studios because for past versions of engine cost was something like 1 mio per project. There was several more like indie developers that has won license on contests, but it's just exceptions.
