> Bigger companies will even force you to take it once you've accrued a number of hours, as it can be a liability on the books

Interestingly, in the UK, managers are also liable for health and safety to some extent. So if you get burned out because you haven't taken any holiday for the last 3 years, your manager has to be able to say "I made him aware he had holiday left and encouraged him to take it" or something along those lines, otherwise they/the company is also on the hook (possibly).

Compared to "unlimited" 28 days is not much at all.

Except it is not unlimited, but instead undisclosed limit, discretionary. In other words, the contract is lying or you haven't read it.

Being fired over taking too much vacation time given the mentioned policy is potentially lawyer fodder.

They'd probably just fire you for 'not being a culture fit' or similar.

It's unlimited in the same way an "unlimited mobile data" plan with a 10GB soft-cap is.

Except unlimited has no real liability and 28 days has a potential value of at least 28 days of someone's salary. From an accounting standpoint it's a big deal.