The last time I left a company, they announced massive layoffs the next month. When was the last time you were similarly lucky? (Sub-question: is getting laid off with severance good or bad?)
That depends on a whole host of factors. In Japan, for instance, it's really hard to lay someone off or fire them legally without a whole bunch of steps. The one exception (and is a lay-off with no severance) is the company is in dire financial straights with proof of that. Often, though, if they want you gone, you take 'voluntary retirement/separation', they pay you a large chunk of your yearly salary, and you go on your way.
In the US, I took a similar buyout once and narrowly avoided needing a second one by quitting before things got that crazy. In both cases, it was a bunch of mergers and buyouts that shook up several companies, one of which I was employed at.