Also consider that the 'huge' ships are actually half scale compaed to the fighters and large ships.
The empire just doesnt have anything iconic that could be even half scaled and still be playable on most peoples tables...
sure lots of boxy EU and relatively obscure stuff but really IMP players want a star destroyer.
The smallest i can think of is an interdictor and even at quarter scale it would be the best part of a metre?
I think someone at FFG a while back went 'hey these huge ships are selling well, lets do a capital ship game'
The only thing they could have possibly done that was well known and 'film canon' would have been a nebulon and that would have been half the table still.

