@ninafeliz brought up a good point, some dessert reservations are filling up, have a look see.
I tested Tomorrowland, Plaza & Cruella's for a party size of 4, 3, 2 & 1 here are the results:
Tomorrowland Terrace Dessert Party
August 16th – Sold Out
Sept 29th – Limited Availability for party of one
Oct 1, 2019 – Sold Out
Oct 8th - Limited Availability for party of one
Oct 10th – Sold Out
Oct 11th - Sold Out
Oct 14th - Limited Availability for party of one
Oct 27th - Limited Availability for party of one
Oct 29th - Sold Out
Oct 31st - Sold Out
Plaza Garden Dessert Party - OPEN availability
Cruella’s Halloween Hide-A-Way
August 16th – Sold Out
Remember guests cancel reservations all the time.