Because he makes to much and signed to long for what he’s bringing.
He can bring more if they find a fit for everyone and until the cap is needed for something better, no reason to move him.
He's a defensively responsible top 9 winger that has produced in a top 6 role with talented players in the past. Having those type of players in depth roles is beneficial as long as you can afford it.
I can see him fitting in with any of Geno, McCann, Cullen, or Bjugstad at center, just need to find the fit on the other side.
Personally, I would like to see a Pearson-Geno-Rust line for a bit, but need to make the other lines work. Maybe:
Jake-Sid-Simon/Horny
Pearson-Geno-Rust
McCann-Bjugstad-Kessel
Blueger-Cullen-Horny/Simon
There are a lot of options that can work. It's up to Sully now to see what works best.