Expansions never on sale as a bundle

I've been a pretty big fan of sins, played it since it first came out (jumped on the bandwagon early). However I don't understand why the expansion bundle is not on sale more often. I see many sales for the trinity bundle (game + expansions) yet never for just the expansions (or at least not often enough for me to have noticed it on sale). As an early adopter I find it kind of strange that there is no impetus to sell the expansions at a sale price to existing users. I would gladly pick up the expansions but it feels kind of cheap that a new user can get the game plus expansions for 30 where as I pay 20 for just the expansions. I definitely paid more than 30 just to get the main game when it came out. Anyone else know if these are ever sold on sale as a bundle?