Those are both the cases where there is a public demand for nepotism, though. People want to see the next generation of the royalty, perhaps more than the kingmakers want to supply it. For that matter, sports is similar but slightly more meritocratic; lots of "Known Athlete Jr." out there in most sports, all of whom are at least good enough to play, but some of them only barely.

You're not giving professional sports enough credit. On the player picking side, it's arguably the last true meritocracy in the US. Teams are willing to take fliers on fringe Jrs because of genetics and maybe the media attention that will come to their team. Otherwise, they always pick the players with the best combination of potential and immediate talent, regardless of background.

Coaching on the other hand, that's as nepotistic as any political field.