Why is the observed rationing of IPOs counterintuitive?

Why is the observed rationing of IPOs counterintuitive? 

Ans. The observed rationing of informed investors is counterintuitive for two reasons. First, it contradicts the optimal IPO mechanism of Benveniste and Spindt (1989), who postulate that, amongst informed bidders, those with higher signals receive their full allocation before any shares are given to bidders with lower signals. Second, it seems to contradict profit-maximization on the part of the seller. An IPO often proceeds by a book building process, during which a demand curve is generated for the shares to be sold. Yet, faced with this demand curve, the seller frequently chooses a price below the market-clearing price.