That is a ton of weight. Forearms or not!
It IS the reason.
When the forearm joint is placed closer to the wrist, it creates a fulcrum more capable for supporting a weight. In actuallity less work(physics) is performed since distance travelled is shortened than someone with a different placed joint.(longer forearm)
I once saw a 60 year old man Behind the Neck press 275 for 10 easy. His arms were incredibly short due to the joint placement.