Because the check box is to affect your traces not anyone else’s.
This is valid only for GVs and Bomber drones (which is something Ive never quite understood why it is so, either both should be able to see them or none, imho). In aircraft however, when I select tracers off, you can't see them either.
What I'm wishing for is a system where I can permanently set which aircraft I want tracers on and which ones I don't. Another alternative would be selecting which gun types you would like tracers on and which ones you wouldn't.
Yes, I'm forgetful and lazy, and only realise 'crap, forgot the damn tracers' after I'm engaged.