or even just adults who don't want to be out that late on a Sunday night. Any entertainment provider is quiet that late on a Sunday. I know that Monday's aside it is the quietest night of the week for a cinema, for example. Also many other places close early because nobody goes out. We got 7800 which is bloody good for 7pm on a Sunday, you seem to be expecting us to get 10k, which is unrealistic.
Public transport back to the Hutt valley is also awful after the game that late on a Sunday. There is a 930 bus which people can rush for which goes to Eastbourne via queensgate. But if you don't live along that particular route (or the train route) you're screwed as there are no other connecting buses. I know of people in Tawa who don't attend for that reason.
Having to rush back home after the game is also no fun for a lot of people. I personally hate Sunday 7pm kickoffs for that reason.
It's a time that is less suited to a lot more people for many different reasons. Much in the same way 2am on a Monday would be even more unsuitable for a lot more people. It really isn't a hard concept to understand.