[Oyk]

Only some staff who works for many years or senior posts may able to get 21 days annual leave.
To enforce it on private sectors is difficult, to more public holidays is more practical, 
it can also boost family time , local spending, attractions for tourists.

It usually starts from 14 days and then increased by one day for each completed year of service till it reaches 21 days.

It is a good way to encourage workers to stay with the company.  

Still, most people do not work for long enough to reach the maximum 21 days.

Most sinkies job hop every 2 or 3 years, many even shorter than that.