"Was it a mistake to place UAL aircraft on these once extremely profitable routes? Is it maintenance? I really don't know the answer. "

First question, do you have any evidence these aren't currently profitable routes? It's amazing when something becomes viral because a statement like this is made on the web.

Second, just look at the age difference between the airplanes you mention. UAL airplanes are older and do require more maintenance.

Third, When UAL purchased the Pacific division from PAA the UAL mechanics were amazed with what the PAA pilots would go with. Each pilot group has their traditions and culture for what deferred items they are willing to fly with. Historically UAL has been a culture of fix it, even when it was determined OK by deferral. Safer? Depends on who you ask.

Fourth, I have no idea about the culture and traditions of CAL pilots and their acceptance of deferrals so my third point may be pointless. Of course I'm sure the Guam and EWR guy will correct me.

Summary: Don't make hyperbolic statements with out the facts, me included.