Doing /! to talk into global chat would take some time getting use to. Maybe just do /! to talk in team chat?
I know it's a team game mode. Everyone just doesn't talk to their own teams; at least what I have witnessed and what I do. People may have friends on a different team and would like to talk them or just talk to other players on different teams for whatever reason.
It's a team based game, right now global chat is a toxic wasteland of hate and abuse. Having to put /! Would just help this situation by making it harder. Team > Otherpeople so it should be easier to talk just to your team.