It's not "extra" money, it's contracted compensation.
The driver stuck in traffic doesn't have the discretion to say, "screw this crowd, I'm bailing on this trip to pursue surge pricing in the next neighborhood over."
It seems the drivers are asking for both sides... If up-front is an underestimate, they want the contracted milage/time rate. If it's an overestimate, they want the up-front pricing.
There is no problem with that. Many contracts are drawn up that way. I think it may even offer a great incentive to drivers to make trips faster.
But it doesn't strike my outrage nerve that it's not happening now.
The driver stuck in traffic doesn't have the discretion to say, "screw this crowd, I'm bailing on this trip to pursue surge pricing in the next neighborhood over."