I thought it was already well understood/researched that it's not the weights that matter, but effectively taking your sets to muscular failure. While one might think "I can do 50 reps with low weights" there is practical aspects to this - you don't wand to spend hours at the gym, and doing heavy weights at 5-7 reps is sufficient as long as you are close or at muscular failure.
Novelty of stimulus is a huge factor, especially as training continues over years. Failure from a set of 20 is very different than failure from a set of 5, and bodybuilders will periodize their training to cycle through the different flavors of stimulus. I think a big contributor might be neuromuscular adaptation. Cycling through those different intensities over training periods measured in months will make this appa…
Some will, many won’t. It’s clearly not necessary.