Milwaukee might end up in a worst-case scenario that has nothing to do with their own decisions. The entire NBA has historically watched blockbuster superstar trades blow up in teams' faces, and now nobody wants to be the next cautionary tale.
If the Bucks do trade Giannis, they're going to do so during an era when recent history shows that blockbuster trades where a team gives up a ton of draft capital for a superstar have generally not worked for the team landing the star. Teams have seen that, and this reality could suppress the market for Giannis in ways Milwaukee can't control.