When it comes to this stuff I stand with the opinion there's very very few big IPs out there that stand up against the scrutiny of whether they are popular with the "general public" without some catch (The catch nowadays growingly being that it's owned by a competitor). Otherwise especially in the modern day yes a lot of things are "niche" or don't get out beyond a perceived subculture, but many subcultures/"niches" are very big and are worth pursuing, especially if you already have the rights to it.
As mentioned the latest Zelda game sold 10 million copies in its first 3 days on the market, that's not something to sneeze at, and converting a fraction of said players into folks who go into theme parks would be pretty profitable. Additionally the whole reason Nintendo entered into the partnership with Universal in the first place has been that while their IPs are pretty popular within video game spaces, they want to grow that popularity with pushes into other spaces, It's not a one way relationship with just Universal calling the shots here.
Even besides all that, much like what is said about some existing or proposed theme park lands, a good theme park land will appeal to the "GP" regardless even if they've never initially engaged with or dislike the source material. My girlfriend absolutely hates Harry Potter but loved the Wizarding World lands for instance.