Sounds funny, but your theory is false. I use GMaps every day to drive to and from work, with a very simple route that's almost all on an interstate highway. Almost every day, it gives me the exact same route (which is so simple I really don't need GPS navigation at all for it). Sometimes, it gives me a different route because of an accident, traffic jam, construction delay, etc., which is why I use GPS all the time, but I see absolutely nothing to indicate that Google intentionally makes my route more complicated than it needs to be. (And yes, these delays are real: this road is under a lot of construction at the moment, and it frequently has crashes and traffic jams in places.)

... especially if they can bring you by some companies who have paid for ads on Maps. Where I used to live, in a grid city, Maps would take drivers down one single street whose only discerning feature from those 2 streets north or south (alternating one-ways) was that it could say "Turn left at the Pizza Hut".