Because guys like Klaus Dornig,Valentino and this guy DO NOT USE SYNTHOL. What they have are silicone implants. THAT is why they use tiny weights,Because it's not real muscle but implants.
Try to follow along and learn to read.
I read pretty well and know a teeny, tiny bit about anatomy and physiology. There's a much better excuse for those guys being weaker than my ten year old. Obviously the synthol either damages the muscle's ability to contract or the constant stretching of the fascia/fibers lengthens the muscle and permanently weakens it.
The constant stretch would cause some creep in the muscles and ligaments. Just like a rubber band loses some elasticity after being under stretch for too long.
Obviously, we're not talking about the other health risks involved.
The implants argument doesn't explain their weakness. A typical guy should be able to curl around 80-100 pounds without a lot of difficulty. Those guys never move crap and probably have decreased range of motion due to either oil or implants. There should still be some muscle under the implants. Women who get implants can still bench press.