Yes, I can see where the pay would kinda suck but they get kickback, and alot of it, from sponsors if the they podium. I know of one rider who won a race and got a $36,000 check from GOPRO because he was sponsored AND was wearing it when he won.
Think about it. Stu made $10M in one year. You know darn well cry-baby Barcia is raking in the $$$,$$$.
Also, Gear, goggles, boots etc are given to alot of the riders.
As an ex-business owner, I was able to afford small things to sponsor racers, it was a tax write-off. A good friend of mine has his own business and sponsored his son and wrote off $27,000. That was bikes, parts, repairs, racing, travel, food and training at MTF.