Because its alot tougher than you think. Firstly Unlike the charedi world where Cherem is done in more modern circles if Cherem is attempted people will wear as a badge of honor and consider it an insult to have been booted. its likely they would become martyrs
and secondly the OU does alot of Hashghcas on many large companies, if the OU would come out against certain people. “Activists” would call the OU “Homophobic” and demand companies disassociate themselves from such a “hateful” organziation and likley the companies would kow tow to the “activists” and the entire Kashrush industry would collapse (Many Charedi kashruth organziations rely on the OU for basic ingridiants)