For the common usage of GPS, mapping - you need ... maps. The GPS just tells the device long/lat, which isn't useful for most people. What you want is to see a little dot on a map with street names, etc..
To be able to do that, you either need to have all the map data on your device (and a way to get updates), or you need to get snapshots dynamically via WiFi/Cell network.
To have the maps locally, would obviously take storage space, depending on the area you want covered, and the level of detail, but also, there'd be considerable $$$ cost.
The mapping companies don't just give away free standalone data, it's surprisingly expensive. They pay telenav (or whomever) zero to use Google Maps, I'd assume. Last time I looked (a while ago) a copy of US Map data was something like $100 from Garmin.
Sprint isn't motivated to incur additional per unit costs when "it just works" if you're within their network.
That said, I've wanted to use Google Maps on my iPhone when I was out "in the sticks" and was plenty frustrated.