BG can be a night time place because it goes out of it's way to make sure there are enough rides and shows to keep people occupied that have nothing to do with animals. Their focus is not to be a zoo, but to be a theme park, with an animal element.
AK, as much as they try to deny it, is in essence a zoo, with a theme park element. A good many of the attractions presented, hinge on live animals. So when these animals cannot work anymore, or find shelter from the forbidding heat, it leaves very little options for the visitors. In the morning, when it's cool, people hit the rides/shows that feature animals. In the afternoon, there is plenty of time in the heat to catch all the shows/rides, leaving really nothing to do at night so people check out early. AK is also hotter than the other 3 parks, and more walking, which gets people tired of the place earlier. EE will certainly help, but I don't think it will be a decision maker in whether AK is open nights like BG is. It would take a lot more maturing in both attractions and restaurants, and a large nighttime spectacular to keep people there after the AK death march.
BTW, to the poster who said Busch Gardens opened in 1980, are you talking about when it became the Dark Continent? Because BG opened way before that, probably in the late 60's at the latest. Back in 1969, Busch Gardens was a small park and one of Florida's highlights, that had no rides (except for the monorail safari) and maybe a train (don't remember), a beer brewery tour, a botanical gardens, and a bird show. That was about it. Like now, the animals seemed to always be a secondary part of the presentation, in constrast to AK's theory. I honestly don't remember when BG became the Dark Continent, so it's entirely possible you are right there, but a lot of people don't remember it's earlier heritage.