Uncertainty makes bids go up. Introducing the possibility that perhaps there might be a second round after a bid turned out to be too low reduces uncertainty.

Uncertainty makes bids go up. Introducing the possibility that perhaps there might be a second round after a bid turned out to be too low reduces uncertainty. Imagine game theory dynamics in poker if an unhappy player could say "well, come to think of it, I guess I did not really want to see, I'd rather fold"