That's a propaganda to make people become employee in their whole life because they keep thinking, if they lost this job, they won't get another one.
Most of the time, if you search other jobs when you still have your current job, you can't change your career. So let's say you're a welder, your top job would be an underwater welder. It's because you have no time to learn other skills and you're already tired.
Only brave people can earn much money, like people invest in something, they spend money to get money. People need to have their own "roadmap" instead of worrying to lose their main job.
That's quite accurate in our day and age. The past few years, especially after COVID-19, there are more than a handful of vacancies, at least where I live, but the shortage in jobs os mostly a worldwide phenomenon. You shouldn't stay in a job you don't wantz you'll find another one, don't listen to employer propaganda that you won't find something better, there's always something better, don't waste your time and life somewhere you don't belong.
We should be grateful, but this doesn't mean we should be stuck somewhere we don't like spending our time in.