One thing I want to add to this site are perspectives from all sides. You're not alone. We're noticing certain current beanies that are hard to find, and we're not talking about ones you might be familiar with. It seems everybody is speculating on which Beanies will retire next. I've heard all kinds of stories, and it's pretty difficult to determine which sources, if any, are accurate.
Nobody really knows.
It seems the folks at TY are sports fans - and there's no doubt that sports have had an effect on beanie development. I have my own ideas that in light of recent events we may also see some retirements. Nobody knows, but at this point, it's as reasonable a speculation as anything else. Nobody knows if there is any discernable pattern to retirements - but like everything else in this world, we struggle to attribute meaning to the unknown. In actuality, there seems to be more evidence to indicate that a design change prolongs the life of a beanie - look at Zip the Cat, which has undergone several transformations.