On the facebook quarantine page I have seen many people asking if their returning helpers can just do govt quarantine, presumably so they don't have to bother to arrange anything or have the 'risk' of having them quarantine in their house. So it may be a considerable number of helpers filling up these needed spots that really should not be.
In the early days, our neighbour sent their helper to govt quarantine - she was sent back in a day and a new rule was put in place saying that the employer had to allow the helper to quarantine at home.

Not sure what changed in the last few days.