$3 million a year times 3 years adds up to significant money, and while very rich by many standards, $9 mill more would make him even richer.
$9 million more, he could use that money to help keep his descendants rich for generations. Trust funds, high level education funds, real estate purchases.
A guy would need to be Bill Gates or Warren Buffett style rich to just walk away from $9 mill. Especially when all you have to do is play hockey in the AHL, where you will spend more nights at your "home" than in the NHL.