That was my biggest gripe growing up in SD - felt like Caltrans / SANDAG abdicated responsibility for developing good transit/bike/ped infra, doubling down on car dependency. It should be a mecca of active transportation given the weather!
There's a lot of low-density sprawl in San Diego county which makes effective transit difficult, and because you have to drive everywhere, sentiment trends anti-bicycle. The previous CEO of SANDAG tried to push a mobility-centric vision but left because of intense pushback from folks who wanted more funding for roads and freeways, rather than transit and bike paths.