The issue I find a bigger problem is lag causing people to talk over one another. I've been on a lot of calls where the call quality was fine but conversations were difficult because it was hard to judge when the other person had stopped talking.
From a technical point of view, that is really the best thing. It works, and sometimes it's the only thing that works.
But if you try to get people actually do it, you run into problems:
(1) They don't realize it's them. AFAIK the system doesn't play their audio back to them, so while everyone else hears the noise, they don't. The one person who needs to take action is the one person who doesn't know action is necessary.
(2) They are distracted. When their spouse is talking, they are focused on whatever their spouse is saying, not on how it affects the meeting audio. Or the meeting is boring and they're not paying attention.
(3) They just don't care enough. They are there to attend a meeting, not fiddle with computer stuff. Some people will never take the time to learn where the mute button is in the software.
Perhaps #1 could be improved, though, with some kind of blindingly obvious indicator in the UI. If "YOUR MIC IS WHAT EVERYONE IS HEARING RIGHT NOW" flashes when your mic takes the floor, maybe you'd notice it lighting up when you didn't intend for it to.
For those wondering, unmuting is a privileged operation that only the user could do themselves.