Extreme Sports? Its their Career dude so they are doing it to their Extreme level with the utmost effort.
They want to experience the adrenalin and the thrill that's there in extreme sports and no other ones.
Because they don't have the patience or dedication to actually learn the skill behind a real sport, so they just get in shape and throw themselves off of stuff...
if dirtbikig is considered a extreme sport then its for the rushes of adrenaline and the wind flying by ur face