It is down to two reasons I reckon.
In the "old" days people had nothing in there room so would pop out for a quick beer to the Naffi/Mess to be social. Fridays were an excuse to finish early to be honest and beer calls were looked forward to all week.
Now, everybody has internet in their rooms and cars on the car park. People just sit in most nights now and play console games and bugger off at the weekend in their cars.
Naafis and messes are like ghost towns now with some closing at weekends because nobody stays on camp.