[Biggs]

ghosting happens all the time in (low/gay) comp play, idk why it can't happen here

Because that's how it's been in competitive multiplayer (PC) games forever. They're using a third party program Ventrillo/Teamspeak and as far as I know there was really no way to tell if someone is using it or not so it was just allowed and it eventually became the norm. That was always my understanding.
On the other hand, in-game chat disables it by default, and for good reason. For example, I don't want to backstab someone and have him scream out my position if I'm sneaky enough to do it without anyone noticing.(or if their team is too stupid to notice) Or if I get a good flank kill as scout, or if I have a nice sticky trap set that multiple people have fallen for, etc. You get the picture.