You did not say which type of hub, the internal gear cable type or the EX box type hub that you have. And you did include any information on your failures. Etc.
I have never had a cable outer housing fail, but I have on a couple of occasions had dust and dirt get into a cable outer near an end where I had to try to clean it out because it added resistance to cable movement.
On dérailleur bikes I have had inner gear cables fail but not on my Rohloff bike. Usually they failed at the end of the cable that goes into the shifter, sometimes putting a bit of grease on the end of the cable can help in this case.
Some people use a lot more force when they try to shift than they really need, I know a few people that seem to think that if they want a lower gear than the bike has, with using a bit more force they will magically create a lower gear, but that is generally unsuccessful.
I am trying to remember if I heard at one time that older hubs were harder to shift than newer hubs, perhaps there was a change in spring tension inside the hub? If so, maybe gear cables are more likely to fail on older hubs? My hub is from 2012 or 2013.
I replaced my inner gear cables a couple years ago on my Rohloff bike, I used Shimano road (not mountain) gear cables, they worked just fine. I am using my original outer housing.
In the photo, this cable is from a bar end shifter that I had on a derailleur fitted bike. When I put a new cable on I made sure that I had some grease on the cable.