Taxi drivers don't do this. Why should Uber?
Because paying more allows Uber to drive supply to meet that demand.
If Uber drivers aren't paid anymore during high-demand times, then there is no incentive for more than normal drives to work during those times to meet the additional excess demand.
Because Taxi drivers are more like employees, and Uber drivers are essentially "independent contractors"
Taxi drivers get paid but have to meet daily targets, otherwise they get paid less, or lose it all. The driver don't collect more during high demand times, BUT even if they did: it's the dispatcher, not the driver that stands to profit.
Taxi drivers are also a regulated monopoly.
However, the Taxi drivers are incentivized since they can meet their daily target more quickly working in a high-demand area, then exceed it, and the profits will go up, and therefore, their commissions in dollars will increase.