Why can I not build a Governor's Manor on this world? Is this a bug?

As you can see, this grumpy goose of a governor is in sore need of a new manor in which to rest his tired feet and eat his slaves, but the manor is actually not being offered as a possible option in the buildings panel. Not even a greyed out entry with some explanation as to why it's not currently doable. Just... nothing?

UPDATE:

I tried deleting the Capital City, and a couple buildings become available, including the Governor's Manor. I'm guessing that's working as intended? You can't build GM's on capital city worlds because that's already considered the governor's seat of power? I'm almost always playing as civs that have the 'Spores' ability so I've forgotten the rules of city worlds. Sorry, can't figure out how to delete the thread now