Type 1 CM isn't a wincon, it only applies to "bestowing" a name upon something, thereby creating it from a state of nothingness. The only combat applicable use for this is changing the name of someone's attack, thereby changing its properties to make it less effective (like making attacks like punching a hole in someone's chest nonlethal, or applying a forced time limit to someone's intangibility). Ofc, this has happened one time in all of canon, and Koishi doesn't have the brain necessary to deduce Gojo's powers and know to conceptually alter them into a state of uselessness.
Also, Koishi is a youkai and therefore has a passive fear/spirit absorption aura, which I don't think Gojo can bypass?