Airport was seeing nearly 3 million passengers a year before COVID. That's a lot people getting a lot of use out of it. Some have a romantic notion of what the island should be. Other can understand the need for balancing romance with progress. I find myself in the latter camp.
Park space isn't romance, its a necessary part of urban life just as much as travel. At the end of the day, this is like putting a toilet in the front yard. It's not a sensible place for an airport. There are several factors that make the airport a bad fit here. 1) Downtown residents have a lack of park space and the island is some of the best urban parkland in the country. 2) Many of the short haul flights that this airport serviced should be replaced by HSR as soon as humanly possible. 3) It's public land that should be available to the public, not just people who have the means to travel. 4) As far as I understand (though someone may have to correct me on this) the flight paths of the airplanes create limits on potential density in the portlands.
I say this as someone who has used that airport and loved it.
The island has roughly 1.5 million visitors annually (up to 20k per day in the summer). I imagine that would change dramatically if it wasn't extremely inconvenient to get to. I love going there but I haven't been in years because it's such a journey.
I wouldn't be opposed to having a certain percentage of the airport converted into housing as it would help connect the park to the mainland and provide a year round set of amenities and people to keep an eye on the park. Plus it would be cool to have a car free neighbourhood served by canals.