Maybe because he's not as good as people think?

There's a couple of reasons.

The first is Soucy's performance. Last season, he was excellent, prompting the front office to reject trade offers for him. The idea was that he would perform at that level again this year and that hasn't been the case. Don't get me wrong, he was still solid defensively and chipped in on offense occasionally, but he had a penchant for taking ill-timed penalties every so often that really hurt the team. Since he played on the penalty kill this was not ideal. Team defense is an area the Kraken may be looking to upgrade this offseason, and Soucy's spot makes the most sense to do so, to find someone a bit more consistently reliable.

The second reason is more of a numbers game. Dunn and Oleksiak are locked in on the left side, so Soucy would have to go elsewhere to receive the pay raise and larger role he is due. Not to mention, the Kraken's top defensive prospect, Ryker Evans, is just about NHL ready. The team will need to have a spot for him to slot into the lineup in the near future.

Overall, the consensus among Kraken fans seems to be that Soucy will be departing in free agency, and the Kraken will either bring in a reliable veteran stopgap at LD until Evans is ready, or look to make a serious upgrade at the position.