1) The weather is just perfect all year long.
2) The cost of living, while high, isn't insane compared to places like the Bay Area or NYC.
3) The public schools are actually quite good in many of the areas without being far flung from the city.
The big downside, however, is that there just aren't many local jobs for techies. The few that exist pay very little compared to the ones in the Bay Area or even a little further north in LA despite the cost of living being on the high side.
My wife and I have talked about moving there for a while (we both work from home) but the big challenge is that we'd have to find other income streams (in addition to our day jobs) to fund a good lifestyle in San Diego. In the face of a pretty tepid local job market and challenges with remote work pay being lower, that seems to be a requirement to make it out there.