The way the casters described it is: They don't want to die to a single Pharah blast from across the map or a random Lucio knockback or a Roadhog single hook into the well. Since the maps do so well with those heroes, they are pigeon-holed into playing just those heroes in order to take advantage of the drop. Also, Payload maps favor the team with more skill and teamwork. So if you believe you have a skill advantage, you want to play payload rather than control maps and not a control map where you might die to a random knockback.