2nd sentence: What I’m about to tell you is probably not the real reason why Google Maps is the “Number 1” mapping service on the web (in terms of site traffic)

2nd sentence: What I’m about to tell you is probably not the real reason why Google Maps is the “Number 1” mapping service on the web (in terms of site traffic)—but I do believe that it’s one of the reasons why. Me thinks you assumed too much.