It's their business model and they are unabashedly seeking another Open. They are also one of the few publicly accessible venues in the region where one can get a US Open branded, par-defending, major venue experience. This may be the Upper Midwestern Bethpage Black.
Outside of Kohler/Whistling Straits and potentially a setup-for-battle at Sand Valley/Mammoth Dunes, there are few publicly accessible, US Open style venues in the Upper Midwest, west of Lake Michigan, and in proximity to a theoretical Chicago-Minneapolis Metro corridor. For those unfamiliar with the area, it is a region with roughly 30 Million people that have no problem driving 4-6 hours, or more, for recreation.
Medina, Rich Harvest, Olympia, Hazeltine, Oakland Hills, etc are all private. Erin is most definitely not a "nice walk" for everyday play, but their public-access, small green, "put all 12 balls in the bag" and slog-it-out-in-the-fescue strategy is probably sound because at this point, you can't take that Rolex Clock away.