You can't fire people for no reason in the UK and probably the rest of Europe as well or you'll end up being taken to court for unfair dismissal. Roles can be made redundant, but it's a lengthy process.

In US perhaps, elsewhere a job signifies significantly greater income stability.

At my company employment is also at will so they can terminate, but they try very hard not to. In practice contractors are let go much more frequently than employees, and when employees are let go they tend to get a soft landing. But maybe my job is the exception.