I think it is a combination of the above posts. The prerequisite is a course that can be made "worthy" of the event (which is tight, tough, firm, and has a backstory), and the ability to handle the logistics of the event for the players. Double sided range, short game area, etc. An ability to handle the anticipated crowd is key, and people with houses adjacent to Merion East have already learned the value of their land for corporate tents in 2013. Parking does not be adjacent to the course. The 10+ minute bus ride seems to be acceptable - granted, the events I'm remembering are PGA, not USGA.
Of course, none of this matters if the members dont have a very strong desire to give up their course for a couple of prime weeks in the season. But I think that desire for a USGA event or major is very different, and perhaps easier to foster, than for an annually occurring event.