With cap space being such an asset in the NHL, especially for contending teams like Edmonton who can use it to make effective tweaks to an elite core, a contract like Campbell's is a total anchor. Even as he plays for the AHL Bakersfield Condors, his contract being on the roster is actively hurting the Oilers when they could be using his money for an effective player.
Unfortunately for the Oilers, with his play being this poor, his long term contract becomes almost not moveable, or it will go for an incredibly high price. According to Oilers insider Jason Gregor in a report today, the team would need to attach significant assets to any trade involving Campbell, to even the costs. Those assets could be a prospect like Broberg, draft capital, both, or taking on another bad contract in return.