First off these guys don't get punched and kicked in the face full force every day no pro athlete trains at full contact every day that would be stupid. I'd rather step into a sparring ring on a daily basis then possibly fall off a roof, have a saw go through my hand, or get electrocuted wouldn't you?
90% of the people I met with missing fingers etc were almost guaranteed to be high or drunk at the time. It doesn't take much to start your own small business and not have to be on the roof or doing the dangerous part of the job. If you want to do grunt work you should at least be learning how to do every facet of the job, saving your money instead of getting drunk and stoned every day, making your own business and having grunts do your work for you while you sit at the office taking calls for the next jobs you will be booking. A lot of construction jobs get forms of hazard pay, just not the lower tier labourers that you find off Kijiji that never graduated high school.
Did you see the picture of the dude with the half torn apart big toe from sparring last week after getting it stuck between floor mats? Just because you're not taking full force punches and kicks every day doesn't mean you're not endangering your physical health every day. People practicing get hurt all the time. You really think that people in construction, on average, get hurt more then UFC fighters?