Maybe you guys with a 'routine' are the reason for that request. I'm hoping to learn how the heck the RO supposed to know a shooter is not still mentally rehearsing. If someone ever gives me a problem about giving a nod or otherwise letting me know when their 'routine' is done, I'll just ask 'are you ready' every 5 seconds until I don't hear 'no'.
Some guys just load their gun, reholster, assume the start position, and are ready to roll. Some have a 'routine' of more or less theatrics and rehearsal and runthrough and whatever. That's fine, but it's often not at all obvious when someone is done with their mental gymnastics.
I was a CRO for years and have worked major matches. I rarely have had a problem seeing when a shooter is ready. They will usually stop and relax, you wait a few seconds and give the command.