Your phone gps does the job.
And what about people who want to repeatedly use their source of maps for a week + at a time, away from civilization, where there are no walls to plug into? Extra "smart" phone batteries are an average of $50.
A garmin etrex can run up to 25 hours on 2 AA batteries, which can be simply replaced.
Also, modern "smart phones" are notorious for having an endless list of problems leaving them unreliable at best. Out of the few I've had, I wouldn't trust the life of a tick with them.
I'll stick with a traditional GPS.