And those people drive on the same roads as you, so you're still affected. Don't you want other drivers on the road to be less likely to t-bone you because they ran a red light?

In the UK, almost everyone learned (and learns) using a manual/stick shift vehicle, and if you learn and test in an automatic gearbox, your license is limited and you legally can’t drive manual. Hill starts and clutch control can be much fun! Lessons and the test involved difficult city situations ranging from extremely narrow streets, through 7-lane roundabouts, country roads both single-track and unrestricted (so 60mph speed limit, but not necessarily safe to drive that quickly - good judgement is required). You must pass a theory and hazard perception exercise, and the testing is government-administered.

In the US it seems almost everyone learns in an automatic vehicle, your license then lets you drive stick with no restriction. At least near cities, the roads you learn and test on are seemingly not 2” wider than your vehicle (measured at the mirrors), the situations are comparatively simple as well. There’s no hazard perception test. In my state, the test is administered by the instructor and not an impartial/neutral party.

I haven’t gone looking for large datasets to support this but it feels like the “I just passed my test” driver competence is going to be different.

I would be extremely happy to buy and trust a system like Ultra Cruise if it could navigate UK roads and city situations autonomously with less accidents/incidents than drivers at the 75th percentile in those environment, meaning with widespread adoption the system would raise the bar, and improve median safety properties of being a driver/participant on the roads. However, I would guess had they not cancelled it, being acceptably good for US driving conditions / better than the average US driver really just means you’ve built a system which can work in the US but absolutely won’t work in London, Paris, Berlin or anywhere else?