Hope this explain's the ruleI believe this rule has been there for a long time.
173. (1) A driver shall not bet in a race in which the driver participates.

(2) A driver engaged to drive at a meeting shall not enter the betting area of the racecourse during the period commencing 60 minutes before the time fixed for the first race and finishing at the completion of the driver’s engagements at the meeting.

(3) A driver who fails to comply with any provision of this rule is guilty of an offence.