Anabolic/androgenic drugs have a great deal to do with this, as does the significance of cummulative volume which no one here seems to be acknowledging.
Perhaps the significance of cummulative volume (tonnage) will become more clear if you consider the total number of lifts which are performed by elite level lifters.
Additionally, Frit you know this, squats to a huge degree, and overhead presses to some degree, play a tremendous role in the training of ANY OL lifter. And squats and overhead presses, regardless of low reps, when performed with heavy weights are going to yield some muscular development.
Olympic lifters employ a significant volume of low repetition sets, add up all of the repetitions and you get a significant volume of time under which muscle fiber is under significant tension. Now, the degree of hypertrophy is relative, sure OL lifters and powerlifters experience muscle hypertrophy, despite the fact that much of training is low repetition, but no where in the same universe as bodybuilders.
Powerlifters, almost across the board, employ a significant amount of assistance work, especially in off seasons, which contributes to gains in muscle mass.
Match up powerlifters, OL lifters and bodybuilders of comparable body masses , all elite caliber, and bodybuilders will make the other two look like preadolescent children.LOL
Sure, the Gary Franks and Mike Ruggerias are huge, and Rezazadeh and Cholokov are giants, but the level of muscle hypertrophy developed in these lifters is NOTHING, and I mean NOTHING compared to bodybuilders of equal body masses.
I have met Scott Mendelson, and I have seen Gary Frank and Ryan Kenelly at a meet, all of whom are 300+ and all can lift incredible amounts of weight, and I have also personally seen and met many Olympia level bodybuilders, Jay Cutler, Paul Dillet, Lou Ferrigno, Ron Love, Troy Zuccolotto, to name a few, and there is absolutely no comparison when it comes to muscular development. You simply cannot compare 300+ lbs and 15-30%body fat with 300+lbs and body fat in the single digits.
Additionally, many powerlifters and OL lifters in the heavier weight classes get fatter and fatter, while bodybuilders of comparable body masses are extremely lean during competition periods. So let’s not view body mass and muscle mass as being synonymous with one another.
Let’s be clear here…There are many ways to develop muscle mass and optimally many methods must be employed, however, there can be no arguement that the repetition method is far more optimal than the ME or DE methods for the sole purpose of building muscle mass.
Optimal is what I am stating here gentleman, not better, or alternative, or exceptions to the rule, or for instance, or what about this lifter and that lifter, Optimal-no more-no less.
The very training of bodybuilders vs powerlifters vs OL lifters when considering their appearance, is testament to this debate. Form follows function gentleman.