Haney is one boxer that is full of pride, Remember before the Ryan Garcia fight he wanted to be the next Floyd Mayweather or better, and after what happened he cannot move on because his first loss, which is a big embarrassment, is something that haunts him even in his dream.
If Haney is in the right state of mind and he wants to get even, he will just move on box again and win impressively against a tough opponent while waiting for Ryan Garcia to fight again because of a one year ban, He cannot move on unless he beat Garcia in the same fashion as Garcia beat him.
A kind of ego where instead pushing yourself harder and try to reclaim your glory you choose to do it in a shortcut, suing Garcia to get his belt back, something that will lead him to erase that embarrassment in paper but fans and viewers witness that fight and there's nothing he can do to remove that he got defeated in an embrassing way.
Only when they make a rematch and he win even not in same way but a win is a win, not in terms of suing your opponent's after losing a fight.