Technically, Japan|did have a carnival PokeBall Park which only lasted throughout 2005, anything beyond that is a meh.
Poképark - Wikipedia
It's proof that a Nintendo theme park wouldn't survive on its own. Our pop culture is so hugely popular in Japan and elsewhere in the world that most of our property takes things over anything else. That's why they have Tokyo Disney Resort and Universal Studios Japan. As an IP, though, while we wish to have a Nintendo theme park on its own, there's just no way it's happening, because you have to be concerned about costs, safety inspections, breakdown, disability accommodations, hiring of construction companies, breakdown, etc, to make sure the park goes smoothly. Nintendo doesn't have the resources to carry out on its own, it just wouldn't survive as a permanent park. They have to team up with Universal Studios in order to expand its IP due to losing out revenue to Sony's Playstation and Microsoft's Xbox.