I think that only people who do not have particularly good relationship with the rest of their team, and either already have or can easily find another good job

I think that only people who do not have particularly good relationship with the rest of their team, and either already have or can easily find another good job. If that's a somewhat stable company, I don't think the percentage would be high. Most people don't like change. If things are okay-ish and you have friends on your team, I don't think a 3-month severance is enough to make you change your comfortable routine. Do some large change at the company, like changing the management structure, moving the company and the chances that people will take that offer will very significantly increase.