Marketing.Seriously what's with these retard companies and removing the shit that is actually good from their menu's BK once again took away Angry Whopper they can eat a dick. Taco Bell needs more Volcano shit. Do these people hate money?
I'm guessing that they have a release cycle planned out well in advance, where they cycle new promotions in and out.
Look at the McRib. There's people that would eat the shit out of it...but enough to keep demand high enough, and constant, for it to be a regular menu item? Probably not. But bring it back occasionally, and for the limited time it's available, sales will be especially high. SAles start to taper...bring in the next limited edition special promotion.
A lot of brewers do that too much nowadays, IMHO. Instead of brewing their standard beers, they cycle through a fuckton of limited editions.