The fundamental problem with public transit in most of the US that has it is that it's not the best option. And when it's not the best option, you get a selection bias towards passengers that most passengers wouldn't want to ride with. Which encourages more people to take other options. Rinse repeat.
I like BART. It's actually really convenient, connecting where I live, where I work, and where a bunch of my friends live. Unfortunately, I have a negative experience upwards of half the time I ride it. Sometimes, it's minor, just some person talking nonsense to themselves in the corner. Whatever, puts me on edge because I lose confidence that this person won't transgress social norms in more extreme ways, but I can live with it. Sometimes the entire car smells like a latrine. Sometimes it's a dude laying across the aisle pleasuring himself. Also not going to kill me, but also is something I'd rather avoid, and absolutely can by not riding public transit.
Uber, by contrast, I only have to worry about the driver making me uncomfortable, and that's relatively rare. Maybe 1 in 10 rides will involve a driver either driving like a maniac, or reeking of BO.
With Waymo, there are none of those issues. Hop in a vehicle, it's clean, it drives safely, and there's no naked lunatics.