NYC of course has a huge % with no car, including avg to even upper income. In KC a huge % still own a car even in city, including many below avg income. Uber is useful on the spot even for those who own a car, Zipcar is pretty much for those who don't have car at all and Zip's target audience is not lower income who would ride bus and not consider Zipcar.
Would suspect those in the middle are so ingrained into Uber they'd stick with it rather than use Zipcar. But there are cases where Zipcar is cheaper and more effective use than Uber, such as suburban and airport runs. Frankly it would be only time I'd use it.
But good to see Zipcar sees enough biz to add the 9th/McGee spot. STL has zero downtown, just airport, which is odd.