I think investors are mostly betting on self-driving cars being closer than anyone thinks. The first company to get rid of its drivers wins.
A partial launch also gives you a bunch of opportunity to iron out other details, like establishing the protocols which allow a rider to call for assistance, or a remote safety driver to take over in a construction zone, weird driveway pull-in, whatever.
I personally wanted to see the patent lawsuit Google had brought against Kalanick to completion- much of the lidar and sensor technology at stake needs to be either licensed using FRAND terms or have each company using its own disparate systems. V2V may be a desired open standard but I'm less than optimistic about its targeted implementation date being a few years away because of this competition.