It's the size of the family along with the literally non-stop golfing excursions, plus the upkeep of Trump Tower, plus the two Trump boys traveling the world on business, plus Mar a Lago, plus the NJ golf retreat, the list goes on and on. Hey, it's Trump, so it's okay.
Fiscally, this has always been my biggest problem with Trump. Not moving his family to the white house put a tremendous strain on the Secret Service, since they have to try and secure in one of the most expensive locations in the US in one of the busiest cities in the US.
I was a fan when Trump said he wouldn't take a salary, it was a nice gesture, but legally, he has to take it (though he could donate it to a charity, which he hasn't done). What I was surprised about, was I was sure Trump would be comping the government at his properties, if he truly was a put your money where your mouth as a fiscal conservative. It could have been a company write off for security/promotion (if he was on site). He gets free press each and every time he travels to one of his locations, so it would be smart, from a business sense to write the SS off as an advertising expense.
Not keeping his core family at the white house is fiscally reckless and selfish when it comes to protection and fiscal responsibility.