I know it may be an important factor to know, but I try to ignore these suggested life spans for animals because, I don't know about anyone else, but I feel guilty if any of my animals don't reach the "minimum age".
It certainly isn't down to them not getting good enough care.
Unfortunately, sometimes it doesn't matter how good a life you provide your piggie, or any other pets, if there is a serious problem with their health, all you can do is your best for them and enjoy all the time you have them.