I think the difference between dumbbell and barbell is just preference often based on the time you've put into each. My dumbbell press is pathetic due to a lack of training.
I think lifting for the looks is part of it. I've also read that most women prefer guys butts to other parts so it's probably a little silly that most guys do more upper body to get the girls.
When I was last going regularly to the gym I knew loads of other guys that worked out. It was near universal that leg day sucked. I was exhausted after doing squats and deadlifts. I'd recover quickly from most upper body stuff. Leg day was still fun but there was a mental battle to put in the effort required. I remember once not being able to drive home after week 6 of the training program Smolov JR with squatting. I pulled over and had to take an hour to recover. I've not had anything close with upper body lifts.
Everyone is different I guess and we are talking about preference.
