1. Most players actually discussing strategy and stuff like that mostly have been known to use outside programs anyways. That's the whole reason why IRC used to be so popular and why discord was even created. Even the games that do have chats that people rely on in-game, they usually are either basically forums, or they only pertain to the one game they are in the middle of playing.
2. Pretty much all of those genres (especially fps, mmorpgs, and mobas) are pretty much strictly real time. Unlike them, gladiabots is asynchronous. Sometimes, I can deploy a match that doesn't get joined until after 2 hours later. Being able to chat immediately doesn't sound like something that could happen often in this type of games
3. I'd rather if gfx worked on the actual game on stuff like giving the bots more reliable information and adding in random maps (even if I think his way of implementation of random maps is silly at best) than spending some time implementing a chat feature. While the discord chat hasn't been the most active, people still can respond often on it, and the the chat on telegram is definitely extremely active.