Breaking was a solution in need of a problem. Breaking, and training for breaking, is painful and may be harmful, so why do it? It is not needed for self-defense, and it is not needed to become a great martial artist. So why do something that does little to make you a martial artist when it may cause an injury that will hamper all your training and may cause problems that will plague you in every aspect of your life until you die. Power breaking is done to impress viewers and to attract new students, since people are attracted to the exotic. Trained martial artists see it for what it is—entertainment.
Doing anything to the excess causes undesired side-effects. Body building is good for all people; excessive body building is not good for anyone. Washing your hands is good; compulsive hand washing is not good. Breaking is good, excessive power breaking is bad.
At one point in his life, Mas Oyama toughened his hands until they were breaking tools, but longer useful as hands. In his later years, he expressed regret for this training, since it caused him hand pain and limited hand movement throughout his later years.
There is no secret ointment or method for hand toughening; the only way is by forging. Different arts have different ways of forging, but they all use the same method, repetitious striking of increasingly harder materials. This method works; hands become striking tools. However, a side-effect forging is that the hands become less useful as hands.