Hardly surprising, given it's installed by default. And that clicking on an address (say, on a website or a text message) leads up Apple's Maps by default.
It's not hard to believe user preferences can be different from the market share of pre installed applications (i.e., I.E.).
Apple Maps over Google Maps on a phone every time for me, and I live in Norway, not in the US.
iOS makes it intentionally much easier to just use Apple Maps and deal with the badness than to use another map App.