In the case of Rey Mysterio (real name Oscar Gutierrez) , he appeared to be like Cena, enjoying the love and admiration of the fans.
Only kids and teen girls like Cena. Other than them no one likes Cena.
About Mysterio failing a drug/steroid test. It is the WWE we are talking about. Everybody there is on roids, painkillers and other substances. That is not a secret at all.
Their job is hard because first of all because they spend much more time inside a plane than in their home and secondly because despite that they do a lot of talking and they just simulate a fight.... accidents happen, the falls are real, there are many injuries that are real.
So it is logical that they take a lot of stuff.