I think leading realtors' opposition to apartments in exclusionary single-family housing zones is often driven by a desire to maintain a preferred lifestyle, not by a desire to fatten their wallets further.
Patrick Siegman
I suspect the California Association of Realtors supports single-family zoning because its leaders are mostly older, wealthier homeowners who live in areas zoned exclusively for detached single-family homes. Like many wealthy homeowners, they want to block new homes in the areas where they live.