From The NY Times:
"The lights never seem to be on and the shutters stay shut.

As the weeks pass by at the White House, the corner of the residence long used by first ladies remains dark, because this first lady does not really live in Washington.

Melania Trump vanishes from view for weeks at a time, holing up in Trump Tower in Manhattan or in Florida, where she can lie low at Mar-a-Lago. Administration officials say she is at the White House more often than the public knows, but when exactly, and for how long, these officials will not (or perhaps cannot) say for certain.

It’s like having Greta Garbo as first lady.

Mrs. Trump is expected to reappear in the capital on Thursday to unveil a postage stamp honoring Barbara Bush, the former first lady, and to attend a ceremony for military mothers. But two people with knowledge of Mrs. Trump’s schedule said she had spent fewer than 14 days at the White House since her husband was inaugurated 108 days ago. Others say even that is a generous estimate. Officials in the East Wing and West Wing declined multiple requests for comment for this article.

That the first lady’s whereabouts is among the most sensitive of subjects in this White House only adds to the intrigue.
The answer is obvious. Melania HATES being First Lady and hates her husband even more. She does (and will continue to do) the absolute minimum to be FLOTUS.