The other factor is that, once calls start getting large enough, it's highly likely that you've got people on who don't do many group calls or video chats, or don't often use the program the organizer's chosen so are more likely to not notice they aren't muted, or not realize that this one doesn't join muted-by-default like their preferred one does, or whatever.
I've noticed a strong preference for actual conference calls, as in, calling a phone number, in certain companies, and I think consistency-of-interface and the fact that no-one, including people from outside the org, need to have a certain program available or installed, is part of the reason.
We use Webex a lot in this way, personally, I get very little or no value from seeing video. The novelty of seeing people in the grid wore off pretty quickly.
I was totally embarrassed the first time I was "that guy" whose eating noises were audible on a huge call. Thankfully someone chatted at me, and I was able to mute. I consider it equivalent to having something in your teeth at this point, and I treat it as an opportunity to do that person a favor by letting them know, instead of condescending to them.
Background noises happen. People take notes using a keyboard.
People cough. If it's a few people interactively chatting, sure, leave things unmuted. In a big group call where someone's presenting, please mute however leet your audio setup is.
Well I use a an actual Shure dynamic mic and unless you get close 3 inches or so it pics up nothing - this is not you crappy laptop mic or 19.99 headset.
