With all his injuries, I think they wanted him to have another year in juniors. The Michaud decision might have sealed the deal.
Who knows. Hopefully when he comes in next year (20/21), he's ready to contribute right away. He probably would have this year though too.
Jost is the exception though. We've had plenty stick around for another 1-2 years after they've already had offers to leave. Oshie, Toews, Boeser, etc come to mind.
Don't forget Joe Finley either.