Because Vancian Force Powers would be so much better, make more sense and TOTALLY not grind things to a halt because you spent your only two force slots of the day jumping across two gaps so you can't use the force to jump a third gap obviously...because...some reason, i dunno. Truly it reflects the nature of the force FAR better then what we have had in any other systems and still retains the narrative nature!
Who needs improving your lightsaber and bettering it over time, reflecting your growing experience and connection to the weapon all Jedi have... When you can, instead, throw your +1 LIghtsaber away for a +2 Lightsaber that does ICE damage! Because that's lore friendly, right?
Who needs this narrative based junk anyway when you can have Grapple rules that require a flow-chart to understand! Who'd want to play something like THAT? HAHAHAHAHAHAHA! WHAT FOOLISHNESS!
Sorry...I Kind of have a violent hatred of PF/D&D's magic system even discounting the balance problems. Plus, as a user of Roll20 I'm just a little sick of people trying to shoe-horn EVERYTHING into 5e.
In spite of my above insane ramblings, I don't HATE 5e (Pathfinder Knows what it did though...). It's a fun system, but it isn't a be-all-end-all system. D&D and PF are good at what they do: Medieval adventuring, and dungeon-crawling beat-em-ups. It can do some other stuff, but you normally have to work hard to make it work. It works alright for the One Ring because, well, it's Medieval adventuring and a lot of the stuff in D&D is Tolkien inspired anyway. So porting it over, while a hassle, isn't going to strain or break it's fundamentals too much. Once you try to deviate too hard from that though, the problems start arising.
FFG's system works for star wars. It's not perfect, but it's far better then the past systems and just works well for what it does. Trying to cram it into a D20 mold doesn't work that well and would require tinkering with the game to such a degree that it becomes something else entirely.
Besides, as the others have said, there already IS a D20 star wars system that people can play. If people want their D20 with a star wars skin, go grab Saga Edition.