They're on public roads because they've decided that deploying their tech is more important than safety.

I don't see any other explanation. We know that it's pretty much impossible to prove the safety of autonomous vehicles by driving them, so Uber (and almost everyone else) have decided that, well, they don't care. They'll deploy them anyway.

How do we know that? The report by RAND corporation:

https://www.rand.org/pubs/research_reports/RR1478.html

  Key Findings

  * Autonomous vehicles would have to be driven hundreds 
  of millions of miles and sometimes hundreds of billions 
  of miles to demonstrate their reliability in terms of 
  fatalities and injuries.

  * Under even aggressive testing assumptions, existing 
  fleets would take tens and sometimes hundreds of years 
  to drive these miles — an impossible proposition if the 
  aim is to demonstrate their performance prior to 
  releasing them on the roads for consumer use.

  * Therefore, at least for fatalities and injuries, 
  test- driving alone cannot provide sufficient evidence 
  for demonstrating autonomous vehicle safety.