a combination of ambition/talent, as well as a good salary i think
same in Germany with these reality tv game shows/competitions, also not very easy to cast a lot of high profile celebrities, usually just a few well known celebs combined with a mix of newer talent to give their careers a boost upwards
however in shows like Celebrity Ninja Warrior or Schlag den Besten (Battle of Champions) it is easy to sign some A-Lister past sports stars though whom still love a good physical challenge
in a olympic year, their RTL also has their own celebrity olympics like RTL Sommerspiele, where they do similar sports events as with the olympics but then with retired sportspeople and other celebrities
former footballer Thorsten Legat (Legatinator) for example, is an ace at synchronized diving or weightlifting
and weightlifting olympian, world champion and euro champion Matthias Steiner is good at almost anything
combined with amazing ''eurosport'' like commentary by Frank ''Buschi'' Buschmann makes it seem like the real olympics
but back on topic, yes you deffo need ambition and talent too to succeed in this entertainment world