Why would the Sabres want to break the bank for Karlsson?

I think the Senators might accept, but I don't get this from the Sabres' perspective. The Sabres aren't Cup contenders, so one year of Karlsson would really just get them a worse draft pick. Then again, the Avalanche went from the bottom of the League to a wildcard team, and the Sabres added Dahlin, so it's possible they make the playoffs, but they don't have the depth or goaltending needed to beat a division winner in the first round. And Karlsson is not signing an extension with the Sabres. He wants to be on a long-term contender, and he really likes Tampa. It's quite possible he re-signs if he's traded to Dallas or Las Vegas, but Buffalo's re-building and Karlsson only has a little while left before he starts regressing, and he wants a Cup.