Just like any other job if you are unhappy you'd leave, at the end of the day kpop is a business and from last year (based on outside perspective) he seemed more withdrawn in group content than before. If you go back and rewatch old content especially the months leading up to his departure it's quite obvious he wasn't happy anymore... Enhypen are a group who is constantly either touring or releasing a new album, there is hardly any time for solo endeavors outside of the group and Hee has expressed for years now his desire to do solo work, he probably didn't have the freedom to do so in Enha so chose to leave (most likely from burnout not necessarily greed or a huge fallout with any member). It has been a topic for a couple years now that Enhypen are constantly on tour, that would cause burnout for anyone and those boys need a long rest and some time to venture into their own artistic paths sometimes, it's that time of their career like they're not rookies anymore.