It would be practically impossible to predict traffic conditions. There's construction to deal with, unexpected collisions, lane closures, road closures, and weather to contend with, not to mention congestion during rush hour.

My tomtom GPS I use informs me of traffic delay issues and suggests faster routes, go Google doesn't need to forecast traffic.

They don't need it, but then again, they don't need cars that drive themselves, and they literally made cars that drive themselves. On open roads too, not just test courses.

It is just an exaggeration of Google's ability to do really expensive things that seem crazy or very difficult.