This is a good topic. What killed the line? HASBRO DID.
They just made too many dumb decisions. Their marketing team seems to be just awful. Every time they have a good thing going, they decide to change it. They make dumb decisions that make absolutely no sense whatsoever.
All they need to do in order for the Deluxe line to be successful is take a look at the ones that measure up as being successes. Hoth Rebel, Snowtrooper, Bacta Luke, Slave Leia, 3PO w/ Battle Droid, Nexu, etc. And then look at the flops; flipping figures, lightsaber spinners, battle pack Jango, etc.
Just make ones that are movie accurate (for the most part), are collector oriented, and come with an accessory that makes a good addition to a diorama or display. It's not rocket science, Hasbro just makes stupid decisions.
I swear, almost any collector could come up with a better Deluxe lineup than Hasbro has done...