Is the 25mph limit a US thing? In the UK the normal minimum (aside from select residential zones where the neighbours complain) is 30mph. Many people would be very annoyed to sit behind a car doing 5 below the speed limit.
I imagine they did 25mph because its slow enough to appease representatives in letting them put the car on the road. Nobody with the ability to actually make this happen is rational or knowledgeable about this, and will behave like psychotic monkeys when confronted with autos, so Google is using every trick in the book to make these look innocent, including Grandma grade speed limits.
The 25mph speed is a hack around US auto regulations, which are far less strict if the vehicle's max speed is 25mph or less.
In California, the default speed limit in business or residential districts is 25 mph, this is also the default speed limit for school zones.