Quote from tripledtrader:
I think the reasoning for the high carry costs is probably two-fold. The main reason is just an excuse to charge an abnormally ridiculous rate, by saying it's hard to borrow. But really is there any justification for charging rates of 50-80%? We're not in a credit crunch anymore. Someone is making a bundle somewhere, and i'm sure it's not the institution lending the stock.
Secondly, it may be in the clearing firms better interest to keep the real thin securities to their own internal market makers. So a high rate does deter traders from stepping onto their turf.