I lived most of my life in SF Bay Area, but have lived in Orange County for the past 8 years. It's quite a stretch to generalize and say "all" of northern cal has better bike riding conditions than "all" of southern cal (or vice versa). I have pedaled extensively in both areas, and each has it's local good and not so good. For example, the central and southern part of Orange County where I live are "generally" very good for bike riding. Lots of wide bike lanes along most through streets, and you can get almost anywhere you want to go in fairly safe riding conditions. Compared to almost anywhere in the US, this is wonderful. I am a daily bike commuter and bike errand person, so I am on the streets daily. Now if we are talking about LA city or much of LA county, it's a different story. Bike lanes and safe on street bike routes are few and far between compared to the OC.

Bay Area has it's good and not so good. I lived in the East Bay for many decades, and on street routes there were a mixed bag. Some good, others marginal. The older areas generally had narrow or non-existant shoulders, so had to find routes where traffic was OK. Walnut Creek-Concord area had good conditions, but there are lots of traffic choke points and not a lot of alternative ways across town.