I'm not a biochemist, so I can't say with any authority, but presumably its to do with the 3rd antagonist and its impact on glucagon. Most of what I have heard is through Reddit communities for the on-market drugs (1st and 2nd gen peptides). The anecdotes from Retatrutide sound like it has way less impact on appetite and for some people that's actually a downside even though the weight loss effects appears to be significantly more powerful.