Arizona is a pure comparative negligence case, so while the pedestrian was likely at fault to some degree, she probably wasn't 100% at fault, which means that Uber would have had to pay damages at whatever percentage it was deemed to have been at fault.

The pedestrian's negligence may have given Uber some leverage, but in a death case, comparative negligence might still have given her family even more.

I don't think any of that is what lead to such a quick settlement, as those aspects were not out of the ordinary.

The best explanation for why it settled this quickly is that Uber didn't want to see all the bad publicity that a suit would bring. First, there's the press conference that the family's lawyered up, with corresponding coverage. Then, there's the news articles on the complaint that has been filed. Then new articles on every new development in the case. Etc. And each time it gets caught up in the media, there's more pressure for political action based on knee-jerk and unfounded reactions to "dangers" of an autonomous vehicle, threatening their project. An early settlement helps avoid that.

Of course, Uber had ot have paid a premium for settling early.