Because the social safety net in the US is almost totally absent. As an European that is one of the main things that keeps me away from ever wanting to work in the States, down there it looks like you're either a successful person, meaning you have a house on which you can afford to pay mortgage, which in turn means that you have a successful job which allows you to navigate the inevitable recessions, or you're always one-step away from being homeless, there's no in-between state where you can live an ok-ish life on a not-so-great job without having nightmares about your economic prospects each and every night.