In some countries (at the least the countries that are European Union members, but probably most countries on the continent) the minimum vacation days is set by law (labor code).

In the countries I have experience with it’s 20 working days per year, sometimes with extra days given based on time spent with the same employer. Also, some employers give extra days from the start. But, importantly, it can never be less than the labor code specified number.

So, unlimited vacation may be a trick in the sense that people will rarely take days off, but you can’t be cheated out of the law mandated vacation. Social protection isn't that bad, after all.