I was the Ads emissary to the Owned and Operated Properties (like Maps and YouTube) in 2010. I managed to increase the RPM by a small but noticeable amount. They used to have ads on the bottom of the screen, which was the revenue source I was optimizing. Then later I was actually IN Maps when Marissa Mayer was nominally in charge. We were trying to develop "maps for business." That all came to naught when they decided it wasn't worth the bother.
Maps is fabulous PR for Google. I can't count the times someone outside of Google said to me, "Oh, I love Google Maps!" But it's a gigantic money loser and always will be.
"What about imputed revenue?" you ask? They don't want to measure that, because then every patent litigant would use it against them, and Maps attracts a LOT of patent lawsuits.