Lucha Libre is worlds different to American pro wrestling and Mistico had literally no training in American pro wrestling before being dropped into a program. On top of that, there are two people on the roster who can work Lucha Libre, one who hasn't done so since the mid-90s in Rey Mysterio and the other being Alberto Del Rio who never really worked the Lucha style and was always bigger in Japan rather than Mexico.
Lucha Libre relies a lot on high bumps that are taken on top of the other person. Your entire body is entrusted to that person a whole lot more than in American Pro Wrestling because it is their job to ensure you land safely and without harm. You can't do that as much in the American style because you have to sell it to the fans as legit more than you do in Lucha. Lucha fans will watch for the spectacle, wrestling fans watch more closely and care a lot more if something doesn't look legitimate.
All that as well as the fact that Cara has been working a frenetic schedule since he debuted down in CMLL who put on three shows a week down in Mexico which he would wrestle on them all. Dude's not young, really and all those years have to be catching up as well as the fact he didn't know the style. It's bad booking more than bad luck that's left him where he's at.
Subject: Sin Cara; Bad or Bad Luck? 
