These two reasons came to my mind immideately.
First reason why home is full of happiness would be love and suport that we receive there. Home is where you are always welcome and supported no matter what. This helps to get through hard times in life.
Second reason is that at home you can spend time with your loved ones. They can give you life advice and share some wisdom with you. Also you can support and help your family members. I think that makes you a better person who spreads joy and love, and this is why home is the best place on Earth.
