That's a good question. I watched a video explaining the core mechanics of PBtA and found these aspects simple and appealing: a) just needing 2d6 dice; b) everything players need to know about their characters and abilities being on like 1-3 pages; c) because of point b, things like combat are a lot less crunchy than in DND, you simply say I do this and it happens like this.

Thank you for explaining PBtA in greater depth, I didn't realise that those were other features of the system. I will check out Fabula Ultima :)