Have you actually looked at the cost breakdown of California HSR? This isn’t all going to contractors but to land acquisition, feasibility studies, parts and materials, etc etc.
I also don’t know where you get the notion that it is representative of public transportation in the US, which is by and large just bus services.
It's an example of how most US transit systems have completely lost the plot. There has been almost no change in the services offered despite smartphones totally changing how services could be offered. Transit systems would rather run empty buses on the same fixed routes than adapt a more efficient, Uber-like, system.
Most transit systems carry dozens of passengers per bus per hour. Fixed route services are more efficient than uber. I’m just having a conversation with your own personal biases at this point.
The major differences between uber and transit are technology yes, but also in the fact that it is a public service that is here to meet the needs of everyone. Uber doesn’t have to comply in the same manner with the civil rights act and the ADA, and it doesn’t have a unionized workforce, which in sum is as much if not more of an impact on the services provided than the technology aspects.