My idea - When the food is nutritionally complete, and extremely bioavailable, providing everything you need, then you don't get bored with it. The brain doesn't force you to rotate it out in search of other nutrition.
I actually spent 2 years as a accidental vegan. I was only drinking the original Soylent meal replacement drinks. I was always hungry, Always craving. I drank so much I was bloated, yet still hungry.