Why Don't More Professional Drivers Use Traffic-Enabled GPS?

A couple years ago, when I first noticed the ability to overlay a traffic report on Google Maps on my iPhone, I assumed that the world of drivers -- especially people who drive for a living -- would take it up very quickly. In a place like New York, choosing a free-flowing route versus a congested route might save you 30 or even 60 minutes on an airport trip.

But I seem to have been quite wrong. In most instances when I take a taxi or hired car to/from an airport, the driver doesn't check any kind of device to see where traffic is heavy and where it's light, even though smartphones with map and traffic apps have exploded in the last couple of years. Once in a while, he'll tune in to the all-news radio station to get a spotty traffic update.

Therefore, I usually now check my traffic app as soon as I get in the car to see what routes are looking good and which are looking bad, and then relay that info to the driver. Why don't more professional drivers use traffic-enabled GPS?