Because people are debating whether it is a resignation (where the employee is in control of events), or a termination ("firing", where the company is in control of events).

Although US has 'at will' in most states, in many respects the way employment issues are judged in the US is similar to elsewhere. So the perspective elsewhere on what counts as termination seems relevant.

You're free to disagree, but that's why it's brought into the conversation.

I think it's good to remind people how terrible the US is when it comes to worker rights. Many people don't realize just how bad they've got it over there.