"We tend to be economical in terms of how we use our brain, so if you know you don't have to memorize the directions to a certain place because you have a GPS in your car, you're not going to bother with that," Small says. "You're going to use your mind to remember other kinds of information."
The brain is eminently efficient. It doesn't work hard unless we ask it to. It's the deeper processing (need to know, new contexts, connections to existing knowledge) that correlates with learning.