I had to look that one up- Not all housekeepers and nannies are desirable enough.Even an unavailable and relatively unattractive woman in the house of another long-term can result in problems.
This can be seen in the case of Arnold Schwarzenegger and his adulterous relationship with his married housekeeper Mildred Baena.
If Arnold had a pretty young single blonde housekeeper, he might have had another five sons instead of just the one.