Females respond to low doses because they carry much lower muscle mass. It's like a man being equivalent to a car with 400hp and a woman being like a Prius. Who do you think will respond better to adding 50hp? The Prius would respond like a mother fucker.
Guys that are undersized or those that experience muscle wasting diseases can also respond highly to low dosages.
Muscle is HP in humans. The more you have, the more it takes to make a noticeable difference or improvement. Do you think a guy that's 250 lean on stage can respond to low doses of anabolics? Hell no. He probably needs high doses just to maintain what he has, and then has to run even higher to gain even a pound or two of lean mass