Doctors have far more job security than you tube stars or actors. Astronauts are an interesting one. The requirements to become an astronaut are set incredibly high. Why? I think it is mainly because so many people want to be one.
In my experience in both the UK and Canada, there are long waiting lists to become firemen.
Generally speaking (and yes, Michael, there are quirks to do with location and timing), how much you get paid tends to go in hand with supply and demand.
Hockey is also an interesting one, as the NHL enforces salary caps. Conceivably without those artificial constraints, the competition for the talent available would result in even higher salaries for the top players.
Note I'm not saying it's a good thing that we've engineered a situation where sports players can achieve these astronomical wages. At the same time, their careers can be very short.
Whilst on the subject: It's also mindboggling how few sports women have the potential to earn big money. Tennis is the main one, where the sport offers parity for men and women. Golf and football (a.k.a. soccer) are growing in popularity and presumably reward, but they pale in comparison to the men's game.