IMO they have. Google maps (at least on Android) now shows me traffic incidents reported on Waze, and it will route me around these incidents in real time as I'm driving somewhere, e.g. "A faster route has become available. Say 'OK' to take this route."
Google Maps already uses some data from Waze (like route closures and accidents) though I really wish the Waze directions were fixed to match Google Maps. A combined app (or at least more unified set of two apps) would be amazing.
Most people don't want anything they like to be diluted or changed. People on HN don't want people from Reddit. People from Reddit don't want people from Facebook. People from Facebook don't want their parents. People in a gated community don't want poor people moving into their neighborhood. People in the city don't want rich folks moving in and gentrifying their block.
People, in general, are xenophobic and like their culture to stay small and untainted. Eternal September happens everywhere. It doesn't mean that Google has to keep two separate mapping applications running. Waze didn't stop to think about their community when they sold the application to Google.
I'm fairly certain directions in Google Maps integrate some sort of dynamic Waze navigation routes. This weekend Google Maps routed us around the highway due to heavy traffic, which is not what it used to do. There was no accident or roadwork, just traffic.