Conventions sometimes have grab bags and freebies full of stuff businesses try to pawn off on you as free word of mouth advertising. 

Coozies or "Can Coolers" are often times one of the things that just get handed out randomly at conventions.  

Why? because they can be useful while walking around from place to place people get thirsty they find some vending machine while talking to some random convention goer, get a soda and remember they have been given about a dozen coozies since 9:00 am, they grab one and their soda pop remains cold enough for the next hour or so.