IT did not close - it had from 11:30 to 5:30 a Phase B closure which is this:
Phase B
No admission of guests with one day tickets, and no re-entering or crossing over from another park unless they have one of the following:
WDW Resort Guests, including The Four Seasons Resort, Swan, Dolphin or Shades of Green, Hotel Plaza Boulevard hotels arriving by bus (Best Western Lake Buena Vista Resort Hotel, The Buena Vista Palace, DoubleTree Suites by Hilton Hotel, B Resort, Wyndham Lake Buena Vista Resort, Hilton), Golden Oak residents and guests.
WDW Premier Passport, Annual & Premium Passholders
Guests with Park Hopper tickets re-entering or crossing over from another WDW Theme Park
Guests with Memory Maker
Guests with dining reservations
Magic Kingdom Guests with reservations for Bibbidi Bobbidi Boutique, Harmony Barber Shop or The Pirates League.
FastPass+ reservations
And it was New Years Eve. Christmas Day you could happily enter at midday (I saw people enter when on the monorail).
Magic Kingdom is the only one though and its Christmas Day and New Years Eve that it does it. The other days it tends to be crowded but nowhere as bad as those days. And even those days the morning and evenings are ok
I will say though I am absolutely used to it now though and dont really notice - we tend to rope drop early magic hours and fastpass so I do everything I want to. There is no more magical time than it at Christmas