The Canucks only just signed Cole last summer, inking him to a one-year, three million dollar contract. He played reasonably well in the regular season, tallying 2 goals and 11 points in 78 games, largely playing a number 4 role.
Things did fall apart somewhat in the playoffs for Cole though. The 34-year-old got into all 13 of the team's game and recorded 2 assists. However, he was a -3 rating and Rick Tocchet clearly did not trust him very much, as he saw a big decrease in his ice time. He averaged nearly two minutes less of ice time per game in the playoffs. It appears that his performance was not good enough for the team to make a serious offer at re-signing him. According to Rick Dhaliwal, the team did talk with the player about a possible extension, but it sounds like those negotiations did not get very far.
To be fair, at this point in his career, it likely doesn't really matter if the Canucks re-sign Cole or not. He's more or less an average bottom-pair defender who takes a lot of penalties. Many Canucks fans are ready to see him go.