Could be a big brain move, or a micro brain one.
Big brain: I'm telegraphing that we'll be letting lots of people go so they will self-select and we won't have to fire as many. I imagine that someone could have this idea, but I doubt it benefits the company in practice.
Micro brain: 'If you have not received notice that are are affected, your are safe! Resume being 100% productive until you receive notice that you are fired at a later time. That is all.'
Having lived through 2001 dot-com bust, I can say that being the retained employee can be worse than being laid off.