Some perspective from a DisneyLand vet and WDW fan...
DisneyLand Resort has the two parks - the original DisneyLand (DL) and Disney California Adventure (DCA). DL has not had a major new E-Ticket attraction since they opened the Indiana Jones ride in 1995. That's right, 24 years ago. In that time DCA was built and opened (2001) then had a major overhaul and "re-opened" in 2012 with CarsLand. All that time DL has had to live with a cool Buzz LY ride (like MK a D-ticket) and a Winnie the Pooh ride. I cannot think of anything else new in that whole time. So from Disney's corporate point of view DL was ready for something big and new. SWGE does not fit at all in the DCA theme and DL was the place. Also, note that ST is at the DL park unlike WDW where it is at DHS (not MK).
Disney could have gone with a different E-ticket altogether and only put SWGE in WDW. But as everyone knows SW is unique like Harry Potter with a gazillion fans. And having SWGE go to WDW (which obviously would be at DHS based its SW history) and not go to DL at all would have created some controversy for DLR - DL needs something new. But even more, as we all know SWGE is just huge and, frankly, having it at both resorts will not subtract attendance from the other resort. It will likely be a large net growth for both resorts.
In short DL needed something new, Disney had finished work at DCA as well as at AK (Pandora - and don't forget EE in 2006), completed NFL at MK, and it was time. Doing SWGE with the same design is a cost saver. I guess WDW vets can feel like they got something extra when the new SW hotel opens.
Now, could they have spun the two resorts as different experiences? Yes, I suppose so. But why spend that extra money? Or, put another way, Disney is successful but they do not have a bottomless pit of money. They are a business and can only spend so much at a time in order to keep a good profit and keep shareholders happy. Would it have been better if they made the two SW Lands different but had to make each one lesser than what we are getting in order to meet their available budget?