I think the main problem with the 4pm closes is that they aren’t always as quiet as is implied. I’ve heard of 4pm close days where rides are still getting queues of 45 minutes or so.
Having the park shut at 4pm when it’s deserted is one thing, but having it shut at 4pm when some rides still have considerable queues is quite another. On those days where some rides are still pulling notable queues, I think it could definitely be argued that 4pm is perhaps too early to be closing.
And as others have said, the 4pm close days may not be a terribly compelling proposition if you don’t live locally. It takes me 2.5 hours to get to Towers on a good run, which can sometimes go up to nearly 3 hours on a bad day. As such, I might not even get into the park for opening time depending on traffic and when I leave the house. On a 4pm close day, that would leave me less than 6 hours. And I know that many are certainly further from the park than I am.
Yes, you could argue that that issue could be prevented by good forward planning and leaving the house early or staying the night in a local hotel beforehand. However, not everyone will have that instinct and not everyone wants to get up at the crack of dawn or shell out for a hotel room to come to Towers.
It’s all very well and good if you live locally and the park is quiet on a 4pm close day, but not everyone lives locally, and the park isn’t always quiet on the 4pm close days, from what I can gather. Also, not everyone will know the park and know how to optimise their day like some on here might, and those folks will be much more adversely affected by a 4pm close.