By all accounts, it was a mutual parting of ways. We didn't strong-arm Marleau into leaving.
His family was moving back to California, and he requested that he be moved out west to be somewhat close, which the Leafs were more than willing to do. They were discussing trades with multiple Western conference teams, because everybody involved knew that San Jose would not be able to take him at that price.
Then, right before the buyout window, Marleau suddenly decided that he was not okay with going anywhere except specifically San Jose, because he couldn't bear to be away from his family at all. Since San Jose couldn't afford it, this necessitated trading this 35+ contract with bonuses due July 1st to a dwindling list of entirely different teams with cap space, before July 1st. 6.25m in dead cap space, and 4.25m in wasted money. This significantly increased the cost of moving Marleau.
Now, months later, he's perfectly fine with moving back out East. Scummy move, and disrespectful to a team that did more for him than he deserved.