For me it is down to the character and level of responsibility of the manager. There are plenty at the higher levels who rarely criticise referees, very much in the minority granted, but they do exist. Graham Potter is probably a good example, Eddie Howe also, and at lower levels I don't think I can ever remember Darren Moore criticise a referee. I'd like to think if I was a manager at those levels I would just refuse to answer any questions about the refereeing performance. After all, what is venting against the referee going to achieve? It won't change the decisions, it won't kick off the proper formal complaints procedure, and is likely to land you in hot water.
I also used to come down hard on players when I managed if they tried to blame the referee. They might get away with it if they'd had a faultless performance, but that rarely happened. My view is that any manager trying to blame someone or something else for his team's failings, whether that is the referee, fixture schedule, a dodgy pitch, etc, is failing his responsibilities as a manager. It is too easy to blame something or someone else to deflect from your own failings.
