I used to have a similar rough patch for the same reason. What's weird is I don't get calluses anymore. Not there, not on my fingertip, nowhere (at least not from playing guitar - I have plenty of callused skin in my palms and fingers from lifting weights).
They stopped forming about 10 years ago. Now I just have what feels like a thicker patch of skin on my fingertips but not what you would call a callus that in the old days might rip off. Ironically I am playing now as much as I did when I was younger and woodshedding.