When you've experienced a few minor illnesses and a bit of short-lived pain, such as a broken limb or two, living forever still sounds great.
I had a (thankfully temporary) condition that resulted in chronic pain for about a year. It wasn't terrible pain, but pain that never goes away wears you down in a way that horrible, but short-lived, pain simply doesn't. After a while you just want it to stop. Before this period in my life I was of the opinion that immortality was worth almost anything. Now I believe that quality of life is just as important, if not more so. I would not want to live forever if it involved even a small amount of chronic pain. I used to think a little pain would be a small price to pay. That was ignorance.
Jobs and Ritchie both died from diseases that probably gave them a good deal of chronic pain over the last years of their lives. I can completely understand why extending their lives was not desirable to them.