Many people including me don't care for the desert style of courses. I have played 2 of the ones on the original list and think they are just better than average, although Troon North is a good tract. TPC at Scottsdale is one of the weakest courses on the PGA Tour, it has great crowds but the course itself is not anything special.
TPC at Sawgrass, Memorial up in Ohio, would be good additions. I would like the WGT to only pick courses that have hosted a US Open, British Open or PGA to be put on the site. SOuthern HIlls over in Tulsa would be a great addition. Take a look at the courses that have had those tournaments and you will see a list of many of the really great courses in the US and GB.