If you are talking about those that actually got under construction, I guess the 2:1 ratio would be a lot lower.
Of my own designs, Centennial in Ackworth, GA is now under housing, and I have a 12 hole course in Lone Oak, TX that never got fully built, and closed last October, although the super is still making minimal maintenance happen as they hope to sell. I also had two par 3 courses from early in my career go under.
In Las Vegas, when Stallion Mountain got reduced from 54 to 18 holes, they kept most of my course, combining 15 of my holes with three others to complete the course. When Wild Wing in Myrtle Beach went from 72 to 27 holes, the only 18 hole course they kept was mine (co-design with Larry Nelson) So, I dodged a bullet with those two, and of course, I never let Cary Bickler or Rees Jones (other architects whose courses did close in those cases) forget it!