The problem with buses and other public transportation is not everyone wants to go to the same place at the same time. So public transportation doesn't work for most people, especially in spread out cities in western states.
Not to mention that some of the people riding with you can be crazy or criminal.
Except for a few unique places that have very high population densities, like New York and their subways, public transportation loses money everywhere.
Even Amtrak between NY and Washington DC, the most highly traveled route, needs subsidies.
If they can get autonomous taxis (and pickup trucks) working and you can get point to point transportation at any time you want, without sharing with strangers, at a reasonable price, there may not be a need for personal cars anymore.
But nobody's really close to that yet.
Especially not Cruise :-).