Spinning up the Uber App is most likely trivial.
Spinning up the legal structure, figuring out all the local regulations and getting permits (it's not 2010 anymore! Many countries and cities regulate ride sharing pretty heavily) in a sane timeline is close to impossible.
And it might be not something that an Alphabet company wants to do risk/ reputation-wise. Better to offload bad press (both related to ride sharing in general, and autonomous vehicles) onto an entity which is already "hated".
And it might be not something that an Alphabet company wants to do risk/ reputation-wise. Better to offload bad press (both related to ride sharing in general, and autonomous vehicles) onto an entity which is already "hated".