This is anecdotal but I believe it’s because your body knows it can’t process food without water. When you dry fast your bodies priority is water so your thirsty but not hungry. Once you start drinking again then your body triggers hunger.
I feel even drinking water turns on all the digestive enzymes or atleast the gut movement… That’s we fell hell lot of hungry… I am so happy that I found dry fasting… Water fasting was like a penance