That still raises the question of why Google picked Nevada to lobby instead of some other state.

I did some quick Googling, and according to this Census Bureau site Nevada has 2.0 traffic fatalities per 100 million vehicle miles compared to 1.4 for the country as a whole; it ranks 10th most fatalities in the 50 states. That could be a contributing factor. Montana, Louisiana, Mississippi, Arizona, South Carolina, South Dakota, Wyoming, Alabama, and Arkansas are the more dangerous states. Those states all have either a greater reputation for political conservatism than Nevada (and therefore more potential resistance to new tech) or lower populations, and most of them are also poorer than average.

In short, of states with relatively high rates of road deaths, Nevada is one that combines a large, relatively wealthy market for driverless cars with a probably more favorable legislature.