Southern California is a great place to live all year long. Everyone should live in Southern California because they don't have harsh winters. Southern California has a great deal of sun. It's a beautiful way to get out in the sun and enjoy life. There is never a dull, cloudy moment in Southern California.
Not everyone should live in Southern California. Sure, some people enjoy mild weather year round, but there are a lot more reasons for living in a particular location than the weather. Culture and identity is a major factor. Most people are comfortable around people they can relate to. People from different geographical regions in the US have completely different outlooks and attitudes.
While it is hard to deny that temperatures in the 60s are extremely pleasant, it is not enough of a reason to live in Southern California. Other parts of the country also have nice weather and places with temperatures that are too hot or too cold have many other non-temperature related reasons to live there.
I have no desire to live in Southern California. Sure, it's a beautiful area of the country with a wonderful climate, but it's also completely out of reach for most normal families financially. Housing costs are ridiculous, and too many people are crowded into the metro areas, such as LA and San Francisco.