Why isn't "Push-to-Talk" (PTT) a standard feautre in all video conferencing softwares?

Because having to keep a button pushed while you're talking would suck, so you want a button that stays pressed and... oh wait, that's what the "mute" feature already does.

@Fast-Nop They instead invented "auto PTT" or auto mute/unmute which has been around forever (and some more), but somehow not a feature in most of the non-gaming software (including discord I believe)

I would sell my left arm for a feature like that in calls that has multiple participants.

I have made a system-wide push to talk button that toggles, or, as it's correctly called by @Fast-Nop: A mute button.

It would be enough if everybody would be muted by default and remained that way until he has something to say.