If I donate a kidney, which I plan to, I run a small risk of the other kidney failing, and I get a few dietary restrictions. The remaining kidney will grow in size to accommodate the work two kidneys used to do, but will still only perform 70 to 80 percent of the work, thus, the dietary restrictions.
I get the sense that the people whose remaining kidneys fail are NOT following the dietary restrictions.
I donated a kidney in July 2017. I am doing well.