Because Google routinely undermines their partners through internal productizing (see e.g. Flintstone/OnHub), and Google has a large self-driving car program.

Because Google routinely undermines their partners through internal productizing (see e.g. Flintstone/OnHub), and Google has a large self-driving car program. There's a clear path from there to a Google(/Alphabet)-owned ride provider regardless of investment in Uber.