What this means is the default is 4 weeks leaves. So you may be on $50,000 and have four weeks leave. You could ask your employer to pay you an extra 2% or $1,000 and drop down to three weeks leave.
Many people will want to keep a fourth week of leave (and will) but equally many would like the option of earning some extra money. This is why choice is a good thing.
And please don’t even try pushing the “Some employers will pressure employees and the poor employees will have no choice” line. Apart from the unlikely motivation of an employer wanting to increase its costs by 2%, you can argue against all and any choice on the grounds that someone may possibly try to pressure someone illegally. Using that logic the state should set all pay rates, as some employers may pressure employees to take a pay cut.