Another comment: purebreds don’t live long? Most “large” dogs live at least 10 years but no more than 12. I’ve not encountered many that didn’t make that.
Although I am dying to know why so many American show GS are dying very young.
You are right in that most of the larger breeds of dogs only live to the 10-14 year range. Just a function of size, mainly.
However, as to your question of “American show GS” dying very young, you are right, to an extent. It goes to what they are bred for (or not bred for). These dogs are bred only to move in a specific manner in the rings, and not to be physically sound overall; nor to have trainability and intelligence; nor to have a work ethic. A lot of breeders don’t follow the European model of passing specific physical tests prior to being considered for breeding (i.e. hip and elbow certification; eye and heart certification, etc.). Additionally, to have long-lived dogs, you have to breed for that trait, and not a lot of breeders do.
So, you end up with physically unsound dogs with no genetics for long life, and with a lot of genetics for medical problems. Not a good combination...
To be fair, you also see this in other breeds, mainly the popular ones (i.e. Labs, Goldens, etc.). Popularity can be a problem.