Waiting for a better deal. He’s got four years left on his contact. What if someone gets injured in training camp and goes on LTIR? What if teams are more hungry at the trade deadline? A lot can happen and Karlsson is under contract. All this trade did was bail out the Penguins from bad players with bad contacts to the great player with a bad contract
That contract is just not enticing, unless the Sharks would eat much more of it which they obviously weren't interested in doing. They are going to suck, and don't want to retain huge amounts of salary when their revenues are going to tank.
He wasn't moved on the last trade deadline, and there were basically only 3 teams interested now with Penguins being the only one continuing to pursue him. You underestimate how hard that contract is to move, coupled with the fact that the Sharks were not really doing all they could to ease that move.
"What if someone goes to LTIR?"
For 4 f***ing years? Remember, this is not just 1 year of Karlsson. It's 4 years of him at 10mil. That's a big ticket.