Why doesn't all the street views work in Google Street View?

The photos are taken by an actual Google van, which sometimes elected an omnidirectional camera which takes pictures every few moments.

The van only drives along major roads, and might take the occasional detour to get to its destination, so there are a lot of roads such it will miss. It would take far too long on have street impression connected with every nook and cranny in none town in reverse city.