Because they offer you severance pay and other benefits which you forfeit if you don't.
Disney is also a special case in Florida because it's THE major employer in the Orlando area. If you burn your bridges there, it's unlikely you'll work in that town again. (Not that it mattered because they were blocking people from coming back as contractors anyway but I think that's a legal issue issue, not a personal one - EG Contractors who worked at a company long term were found to be defacto employees by a court ruling against Microsoft several years ago - To get around that ruling contractors have to have a "rest" period of more than a year or else they might get to sue the company. I suspect Disney's actions for not hiring back the employees as contractors right away is probably to get around that.)