The explanation behind this is actually pretty disturbing. Due to selective breeding the growth hormones we feed chickens in America, the chickens become fully grown much earlier than usual. It’s like the equivalent of becoming a fully grown adult by the time you are the age of five, but you still have the mental and muscle capacity of a five year old.
Between 1957 and 2005, chickens raised for their meat quadrupled in size due to selective breeding. They grow to their slaughter weight in just 6 weeks, and their legs often struggle to support their own body weight.