I'm not so sure, for most vehicles the ideal location for a dashcam and the ideal location for a GPS are two different locations, add to that the camera can be pretty stealth and the type of thing you can leave in all the time as you would want to so it's setup to go all the time, the GPS on the other hand is the type of device you don't leave stuck on the window sometimes, parking lots etc, as soon as it becomes something you have to keep taking on and off it becomes a chore and you'll find the time you get lazy and don't stick it to the window and drive off will be the time you need it most
I'm sure there are some scenarios where it might be a reasonable option, in a truck, delivery vehicle etc perhaps, there's obviously some sort of market for them or they wouldn't exist, there are others around also