Perhaps the original concept of the lounge system has been lost in the execution.
For instance, take the Red lounge. It was presumably planned in the days of Virgin West Coast so the colour was appropriate. The original idea might have been that all Virgin WC services would leave from Platforms 1 to 5. The First Class Lounge was positioned suitably.
A similar allocation would be a lounge for all Cross Country services, and a third for Birmingham commuter ones.
That makes sense, but was sabotaged by the operators who decided that it was, for instance, impossible to have Virgin/Avanti WC services leave only from Platforms 1-5.
A particular oddity is, if you are in the Avanti lounge on Platforms 1-5 and your train departs from Platform 6 or 7, the entrance to those platforms is just behind a glass screen that prevents you accessing them. The '6' sign at the top of the escalator is very close behind that glass screen. You either have to go a circuitous route to the right dateline, or go against the flow to the 'B' end footbridge and back again. There are three lounges but only one through walk way, so it would seem to have been possible to only have two lounges, if that's the reason.