America has very low unemployment and median household incomes are among the highest in the world. You get to continue your existing health insurance 18 months after you quit if you wish, you just have to pay for it. Most people can and if you can’t then the government pays for it.
While getting terminated is disruptive, it isn’t the end of the world for the typical American. The relative ease with which most people can get another job is also nice. It is an economy that is structured under the assumption that people will move between jobs and minimizes the friction in doing so.
I have seen the “having a contract” thing abused many times in many countries in Europe. Thanks, but no thanks. I have had that contract multiple times and I don’t want that contract. That safety blanket comes with heavy chains. I’ve seen those contracts used to stifle far too many employees to condone it, employees deserve better.