Can't answer your question definitively. but I remember visiting the site in the sixties, so its been over fifty years, To the best of my knowledge the stations have never shared common ownership so their sharing of a transmitter site has been puzzling.
According to the below article the move of KFWB was in 1965 (my visit was a few years later), but no explanation as to why.
https://www.fybush.com/sites/2006/site-060714.html