It is neat to see all the roads you normally drive in the self-driving videos and it is almost taken for granted that they are here [1][2]. Chandler has always been in early on technology due to many reasons but that lots of programmers/engineers work here due to intel historically, projects like Iridium started here, also one of the first places to get cable/broadband internet in the 90s.
With that said, Chandler is very easy to drive, square roads, good weather, clean roads, clearly marked and kept up, minimal freeway needed etc. It is a great place to start but still lots for the cars/algos to learn, however it IS happening and I see it everyday.
Many of the videos are around Chandler downtown that is a bit busy and has lots of movement/pedestrians[3], so that is good that it is able to navigate that, it is close to busy urban environments.
[1] https://www.youtube.com/watch?v=aaOB-ErYq6Y
[2] https://www.youtube.com/watch?v=B8R148hFxPw (360 degree experience)