The Santa Fe did want to construct what would have amounted to a railroad subdivision at Tejon prior to WWI but did not have the resources in a time when you had the rr's taken over by the government and thereafter the obvious rise of the ICE auto and truck and concomitant highways. So they cut a cheaper and quicker deal with the SP for trackage rights over Tehachapi.

Historically if things had been a little different at the time the Loop was built - say a much bigger LA - the Grapevine might have been breached by rail when money was gushing to a rail system that enjoyed no competition.