A sufficiently heavy weight (I'm talking about optimal TUT also, so no heavier than about true 5-6RM) would require too lengthy rest intervals to repeat, prolonging the workout unduly (considering the unwillingness of going to the gym more frequently than 3 times per week). On the opposite extreme we have BB-style 3-4 sets with fixed short rest periods using lighter loads which are a bit impractical to implement in a semi-crowded gym. You tend to miss the proper time to do a set, get frustrated with potentially skewed progress tracking, etc. When you use different exercises, though, you no longer carry the psychological burden of the decreasing strength between sets, you concentrate on each exercise and do your best, having no idea how the load would feel when you're fresh. Especially when you alternate between sets on different body parts giving the just-worked body part some more time to rest.
Well I can appreciate the psychological components of your hypothesis. Horses for courses etc.