Interesting that this question is being raised elsewhere.
The only reason I can see for two nights is "we've always done it like that". This however is a recipe for disaster. Keep on doing things just because you've always done it that way is not really a reason.
I never really understood or had it explained where the 12 hours/month came from, as we are not employed, not salaried and have no contract to enforce the 12 hours rule. Also the 12 hours rule only applies to uniformed staff. Like so many things it seems it's a club rule and we just blindingly just go along with it and not question it.
Back in the early days ADCC/ATC IIRC my uncle (member when the ADCC changed to ATC) said they used to meet once a week and spend every other weekend at the local RAF airfield. They couldn't do more than one night as there were 140 of them on the squadron and were split into 3 flights. They did all the training they had to and he said the staff used to be assigned to a flight, apart from the CO.
The organisation seems to do far more things at the weekend than I remember as a cadet and I did a lot of sport for the Corps, which meant doing things at the weekend. But there wasn't all the training/courses that staff do or training/courses for cadets. We did the occasional AT thing at the weekend and in the football season a crowd of us would meet up for a kick around on a Sunday morning.
When I posed this a few weeks ago, the main message seemed to be "we've always done it like that", so only a historic precedent and there's so much to get done, which begs the question why do we (or more correctly HQAC) seem to think we need to do so much?
There is a lot of white noise emanating from the top about valuing volunteers, maybe the one way to value them is to reduce the time burden. Make it so there is only the need to do one night a week. Today there are so many shared buildings, doing one night would make those arrangements far, far easier.
Adults seem to have much busier lives now and the cadets seem to be under constant pressure from school, that maybe one night a week, would make the organisation more attractive generally to adults and parents. Although probably not wanted when they are looking to cut costs.