Not if you leave them stock, they're not. With a few mods a GSPD's stock range of 550kms can be extended to 700kms. But that's niether here nor there. The Oilhead GS1150 used fuel like mad. One of the reasons I despised that bike.
Fuel efficiency of the H-D motored Buells is pretty impressive, and one of the reasons I like them.
There's no reason why more modern motorcycles couldn't be more fuel efficient. BMW's taken the issue seriously with the mapping\fuel delivery of their 800 series parallel twins. Peppy 85hp machines that deliver excellent fuel economy. Looks like Honda's beginning to take notice, too.
There's lots of variables involved and it's a complicated subject, but you're probably correct: Historically, most people don't really care about fuel efficiency when buying a large displacement motorcycle.
I'm thinking that might change in the future.