The 85% is probably about right, not sure about the 'due to physical problems' I think a lot of it is people think they can work a 40hr week at a very lucrative hourly rate and make lots of money, when in reality about 20hr of hands on work per week is generally considered full time due to the strain on the body, which means you don't make lots of money. If you do try the 40hr per week, you either don't get anywhere near it, or if you do reach it, you burn out very quickly. Schools don't seem to let on that 20hr per week is a pretty full workload. Schools tend to imply you can graduate and make lots of money immediately - in most cases it takes time, and often people give up.
People that make lots of money in massage are NOT doing the hands on work, they're a business owner, renting rooms, employing others, teaching, whatever, they're not massaging, or they're not massaging that much, it's all the other business income money making them lots of money.