He wanted to go to a playoff team, but he was tired of losing (which I found the Ottawa situation ironic). I understand the reasoning from Duchene's POV, he spent 9 years and a majority of his prime years with the Avs and has only played in 8 playoff games. The team finished dead last by a large margin and there was basically zero expectations heading into this season. Plus i'm sure he realized teams trading for him wouldn't be rebuilding teams, but playoff bubble teams or contenders. Even if that didn't happen, worse case scenario in his mind would be he'd be going from one lottery team to another lottery team.
I don't have any ill will to Duchene and I understand why he wanted out, but I can only imagine what he'd be thinking if the Sens miss the playoffs while the Avs make it this year