For what it is worth, Amazon has built (as opposed to just rent) very large buildings in Seattle, WA and Bellevue, WA. It could be a sunk-cost fallacy sort of deal going on here. They even built giant ~~testicles~~ glass spheres with plants in them.
I don’t think I buy that answer. They’re on the hook for the money either way. Ego?
They lease a lot of buildings too. Paul Allen owned a bunch of the area.