* Because I may not have an internet connection near my destination
* Even if I do, my maps app has a thing for taking me to the wrong place. Anecdote: some friends and I went biking through a popular bike road through the woods. When checking the route on their phones, all they could see was "you are here", and nothing else because apparently the road didn't exist.
* Paper is more reliable than electronics: a paper map will survive a fall, water and mud, and it will never run out of battery.
I don't deny the usefulness of electronic maps for daily use, but I honestly don't trust them for visiting unfamiliar places.
But I'd find a traveler foolhardy to not at least consult a map ahead of time when visiting some very new, distant place. The good thing is that it's normal in the US for gas stations to all carry local maps. So I'm usually not more than a few minutes from being able to stop off and get my bearings if needed -- last I had to do that was in a tricky part of NC (damned business/non-business routes) in 2007.
I do similar stuff with mental arithmetic, to make sure I can, and exercise it.
I think the main reason I go straight to fancy electronics when driving is because I don't really like driving all that much,and want to make sure I get to my destination as quickly as possible. I'd rather save the pain and effort for other things.