If professional pilots can operate in Class G airspace in cloud without it being “one in, one out”, then why can’t air traffic controllers operate in this airspace with the same rules?
Because they are not required to apply procedural separation standards until the aircraft is identified, ATC are. I don't believe you understand how restrictive they are. I hear (heard, I'm not RGS) pilots nose to nose, and negotiate a rate of climb/rate of descent they are happy with to separate their profiles, ATC only have 10 minute before time of passing. Which is not practical, so 'one-in-one-out', when you're taxying and the Seasprite is inbound...