If they want a big salary and can't deliver enough value for the company or the company can't extract enough value from their skills (see above why) they might be let go, but this happens in countries with poor worker protection, like the US.

Companies in EU countries have the opposite problem, they can't easily dismiss employees, even when perhaps justified.

I wouldn't want to work in the US, it's too darwinian. A company shouldn't be able to dismiss an empoyee just because there's someone cheaper available.