The captain stated on multiple occasions that he wanted to be a Canuck until the time he retired, though Patrik Allvin and Jim Rutherford did not fulfill his wishes. Canucks management traded away one of the league's top face-offs winner, goalscorer, and two-way center, and here's why :
The Canucks had previously signed J.T. Miller to a $8M x 7 years before the beginning of the season and they had stated that they weren't willing to go above it for their captain Bo. Horvat has been on pace for a career high since the current season started and now that he's off to the Isles he'll have an opportunity to settle new marks for himself.
Rutherford repeatedly stated that they had a strong offer on the table for their captain, was it good enough? More likely than not, the Islanders will have to offer him more to keep him around.