They're separate because Waze has a reputation of giving more "aggressive" routing, and has a social aspect to it. Stuff that really doesn't belong in Google Maps.
Like making you take an extra 10 turns, take a longer route, and drive on too-narrow roads, to potentially save only several minutes of being stopped in traffic.
I would immediately stop using Maps if I had to deal with any sort of social media infiltration. I already stopped using it in favor of Apple Maps if I have to do transit routing (Apple's a bit more accurate with timetables).