Yup, it is genuinely convenient that Waymo doesn't rely on an unpopular payroll tax for funding while the bus system does
To be fair, it gets far more subsidies from the government in general by simple virtue of being a car, they're just A) longterm and thus assumed and B) less visible in general. So I'd say the connection between transit and controversial taxes is arbitrary, really--I'll grant you "convenient", but definitely not genuinely-so!Portland car infrastructure in particular does get a little love from me just because of how damn impressive some of it is (namely the mountain passage to the west and the complex bridge interchanges on the east side) but it's still car infrastructure.
How does Waymo get subsidies? If I ride in Waymo, does that mean I get subsidies?
Road maintenance isn't a subsidy, it's a collective good that buses also benefit from along with many other types of human transport. This is separate from the cost to the government of running a bus system, which is exactly what large numbers of people really don't want to pay an additonal tax for and are therefore voting against.