You were correct in the first sentence.

It shocks me at how many people don't understand that sports betting odds have nothing at all to do with how good a team is, what their schedule is, or what the expected outcomes are.

The algorithms that are used to determine odds are designed to predict how people are going to bet. They don't care at all what actually happens, what teams win or lose, or any of that. All they care about is how people are going to bet. The goal is to create even action so that they make money regardless of what the outcome is. The house always wins.

So in short, these odds have nothing at all to do with what Seattle's chances of winning a SB are and everything to do with how much money is being wagered on them.