Google wishes it wasn't 95+% an ad company. It's a highly profitable space, but it leaves them vulnerable in the long term.

Google is entering into the delivery space (Google Shopping Express) and into self-driving cars, both which are similar to or complementary to Uber's business model.

As it stands now I'd agree, but Uber's the first market that'll be overturned by self-driving cars.

Commercial trucking is the first market that will be overturned by self-driving cars. More predictable routes, do not have to deal with passenger misbehavior, higher total profits to absorb early-on technology costs associated with creating the self-driving vehicle (LIDAR costs and whatnot).

Google has other realms that could benefit from self-driving cars, not just ride-sharing/taxi. Why have separate fleets of vehicles if you can have one that does taxi services, shopping deliveries, and data collection (street view) at the same time?