I think there are at least two reasons:
- Some people don't have reliable access to cell phones with map/GPS functionality.
- Some people just prefer using a paper map.
In fact, I fully encourage the use of analog stuff - paper maps, writing on actual paper, even analog music, stereo, and recording gear.* So much gets lost in digital.
*I actually owned a tape deck and a Tascam 424 mkIII (which broke unfortunately, to no fault of my own), and we have countless vinyls in the house. So yes, although I'm young, I still have experience with analog stuff.
EDIT # 1 million: When I was 8 years old, our family drove all the way to Québec, Canada on a paper map. Sure, we had GPS, etc., but my parents chose not to use it.