I read it as 75% decided to ignore that email. I guess one way to interpret that is that they decided to quit, but I don’t see it that way. It’s more like an ultimatum that they refused to respond to.

Checking that box was agreeing to work “hardcore” and add a bunch of hours to your day. I imagine a lot of people receiving that email guessed that their colleagues would also ignore the box and figured “he won’t fire all of us, right?”.