But they work really long hours

For the first 2~3 years, they are not making more per hour.  Their salary is normal (under 10k), but if the bonus could be from 50% to 300% so they making a lot that way.  After the first two years, more than 70% are gone.  Basically if you only get little bonus (like 10~20%), you are not fit for the job.  Better quit.