Because if Bill Gates is paying $150k for bananas, my expected value as a shopkeeper is maximized by not selling you my limited stock of bananas at $0.50/each and instead waiting for the remote possibility that Bill Gates walks into the store instead. It's not socially optimal for bananas to rot on store shelves when there are willing customers at a lower price point, but this happens all the time in dynamically priced markets.
This comes up frequently in housing, for example.