Crying babies are a whole different ball game. Babies cry--especially when their ears hurt and they don't know why.
It may be that he was a first child and the mom was nervous flyer. Just the fact that she was upset about his/her crying on the flight may have made it difficult for her to relax enough to quiet him/her down.
I was once on a flight sitting next to a very freaked-out mom with a crying baby. I offered to walk him for her and the minute I picked him up, he fell asleep. I am sure that part of it was because I was calm and relaxed and was able to communicate my relaxed state through my touch to the baby. It may also be that he had just cried enough to finally pop his ears.
Since none of us can account for our own behavior as babies, we should probably cut them as much slack as we possibly can. They have no idea if they are in first or coach.