I don't think it's a personality change, at least insofar as personality is separate from neurochemistry. Ghrelin and dopamine are strongly linked, and dopamine is our central reward-seeking driver; GLP-1s generally reduce ghrelin production, which I suspect helps remove you from a state of being constantly primed for reward-seeking. I noticed this firsthand when I went hard keto for the first time, and could suddently for the first time tell a significant difference between "I want food because I'm hungry" and "I'm not hungry but want food because it's pleasurable".