I hear what you're saying. However, in addition to the Premium Terminal 'philosophy' I think entry requirements may also have been influenced by the physical size of the lounge. There are barely enough seats for when two QR flights overlap slightly, so allowing non-premium passengers in would have swamped the place.

At least we can still access the Skyteam lounge, at one stage I was worried even that would be denied to Elite Privilege Club members!