Hard to pinpoint why he had a harder time recovering after the second kyphoplasty. In addition to being 2 years older at the time, he has had rheumatoid arthritis and anemia for many years, was diagnosed with MGUS after the first surgery (this can affect bone marrow and strength), and was also diagnosed with pulmonary fibrosis during the year in-between kyphoplasties, and needs oxygen upon any exertion as well as overnight. Not able to do bone-strengthening exercise any more. So there are a lot of things going on, in addition to the osteoporosis which should probably have been addressed by the doctors much sooner. He has had severe kyphosis (they call it hyper-kyphosis) which developed before his first fracture, and his spine is probably under constant pressure of being bent-over at a 90-degree angle. It's probably the combination of all of these things.
It's hard to say whether he's healing as well without the 3rd procedure, because he was probably not completely healing from the second procedure on 2 vertebrae when he developed the last 2 of 5 total fractures.
Keep in mind that he really needed the first kyphoplasty because he was in such pain and couldn't get around much. It was such a success, we went on vacation just a week and a half later, and he also continued going to his part-time consulting job for the next 2 years.