Equibase usually has morning lines the earliest. After the entries are drawn, the info gets sent to the information providers (namely Equibase who then sends the info to other information outlets). The morning line maker handicaps what he/she thinks the public will bet, but this takes time. These morning lines are then transmitted to Equibase and on down the line. Perhaps the Santa Anita M/L maker has a lot on their plate and makes the line as soon as they have free time.
Disclaimer: I only know about this from my experience making greyhound morning lines, thoroughbreds may be different.
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