Why would anyone live in a place where you freeze your balls off for half the year?
My choice is San Diego...
I've heard San Diego is great. I've also heard it's super expensive and becoming even more so.
The answer to your question is low costs of housing and living, tons of recreation, good sense of community (everyone deals with that shit together every year), low crime, and changing seasons for activities that are varied as well as new scenery every 3-4 months. My knowledge is limited I admit, but from what I've read and seen on TV of San Diego, you only have the recreation part it seems.
My question back to you, is why would anyone want to live in a place where the seasons consist of rain and sunny with drought? I guess you could include earthquake, mudslide, and wild fires as seasons so there's that.

When reading the criteria, I though it would be a better list if Demographics was left out. To me it's racist to include that. It should be if you removed color and ethnicity; what places then have the best economy, affordable housing, best food choices, most recreational activities for all age groups, lowest taxes, low crime, well managed budget, personal freedom/tolerance, etc.? To me those should be ranked highest as if you have all of that people from all walks will eventually come there.
I looked closer at their definitions of categories though, and Demographics is fine. "Social and Civic Capital" needs to go though. Other than crime, even the site admits it's hard to measure. Their measures are either subjective and/or require a person to honestly answer (whether they voted) or decide if they want to answer (volunteering). A lot of people either lie and say they do one/both, or want to keep those things private.
https://livability.com/best-places/ranking-criteria