The main reason is that we have a limited data plan on our phones so using the phones for mapping can easily over run our data plan. Looked at unlimited data but too costly for the amount of time we would use it. I hate to buy an another navigator so just checking on upgrades. From what I saw, it appears the whole radio would need to be replaced and that's too costly. So looking at Garmin.
I have a limited data plan and use Google Maps/Android Auto for navigation all the time. I'm currently vacationing out of state and use it almost every day. It uses a
lot less data than you may think. Just don't ever use the satellite view. The map coordinates are binary data and don't require a lot of data usage. You can travel about
457 hours of driving using Google Maps for 1GB of data use. That's a
lot of driving time. Waze uses even less, about 1,449 hours for 1GB.
Additionally, if you plan to use it mostly in specific regions, you have the option of downloading the map data for those regions once, and then it stays on your phone and uses much less data afterward.
Try it for yourself. Use it once or twice and see how it affects your data usage.
I have the RAM nav built into UConnect 4 and believe me, it is nowhere near as good as Google Maps. UConnect 5 is supposed to be better but I doubt it's as good as Google Maps which has far more development into it. Google Maps will be better and much easier to use, especially when used with Android Auto. You can even use voice commands by holding down the voice button on the steering wheel which will route your voice commands over to Google rather than UConnect. The voice command feature for the UConnect 4 Nav is barely functional whereas Google's voice commands are incredible. Rather than a highly limited, almost nonfunctional voice command set in Uconnect 4, Google's voice commands are one of the best in existence anywhere.
If you want the best in navigation, Google Maps is far superior. The Uconnect implementation for Android Auto is excellent making Google Maps one of the best choices for navigation in a 5th Gen RAM. Best of all, it's free. Take all the money you were going to spend on Uconnect Nav or a Garmin and save it for something else.