Six months on from sensationally snatching Joshua's IBF, WBA and WBO heavyweight belts, Ruiz was on the wrong end of three lopsided scorecards on Saturday as he suffered a comprehensive points defeat.
There had been significant surprise at the weigh-in when Ruiz tipped the scales at 20st 3lb, more than a stone heavier than he had been for the first fight.
In a post-fight news conference, a sheepish Ruiz admitted "the partying got the best of me" and apologized to Robles and his father for his poor preparation, adding: "I should have listened to them more. I shouldn't have put on all this weight."
Robles told Seconds Out: "We had the time, we had the sparring, the proper sparring, I believe, but it's up to the fighter. It's definitely up to the fighter.
"I'd rather not discuss that because I don't want to make it seem like an excuse. The better man won, period. Unfortunately, as Andy said, he should have been more committed, he should have trained harder, but what are you going to do now?
"You've got to get back to the drawing board and if he really means what he says about coming back to the gym and training hard then I believe he's definitely a title contender. He can definitely give everyone a run for their money."
Defending his own work, Robles added: "I don't think I lost the connection with my fighter, I just think it's more him, it's more the individual. The individual has to be disciplined, you got to be hungry. I can't want it more than him. He's got to want it."
Ruiz claimed increased media commitments had hindered his preparation, but Robles said: "You cannot let the situation control you. There's 24 hours in a day when you can go and do a press conference or show up some place but then you still have the rest of the day to get back to work, to get back to business."