CSLs are not used to draw parked aircraft, they're only used for other 'live' traffic.
Are you using any add-on scenery for SFO? If not, this is expected behavior. If yes, parked aircraft assignments depend on:
1) the scenery creator tagging the parking locations accurately (or at all), and
2) you having a matching model for the airline assigned.
You can address #1 by using good-quality custom scenery (although not all payware has accurate gate assignments, looking at you Drzewiecki!)
You can address #2 by installing the
MisterX Library, which has many parked aircraft types and liveries that X-Plane can find to draw for you.
Even if you address both of those, you'll still occasionally see oddities, like a VisionJet drawn parked at a gate, or those damn Air France CRJs parked in the USA. I'm working on a new project that will try and address these on a region-by-region basis, but my spare dev time isn't common right now. I'll be sure and post in here if it ever comes to something.