>>214523035
Note the contrast between his last days and the last days of the first Dusk you ever see in Season 1. This one wasn't surrounded by the comfort and support of his brothers or the former stability that used to uphold the empire, so his fears were never tempered or assuaged in any meaningful way. His last meal was alone. He was left to his thoughts, and he went mad.
You kinda get the sense that All Cleon clones get the same kind of fearful and nihilistic when they reach the end of their lives, and it's only when they have a decent enough support situation that they don't meet their end in terror (or in this case turn into Darth Darkness)