Good question, not sure on the reasoning.
Limited can start hammer back with safety on. Not sure why a DA/SA gun in CO cannot.
Maybe they think it's an advantage and want you to have that long and heavy first pull, LOL.
The odd thing is that with a multi-string stage, it isn't a DQ if you holster the gun with the safety on and hammer back(In CO). So, it apparently isn't a safety issue.
My best "guess" is that they want it on even ground with striker fired guns.