Disneyland is also a park that's always full of passholders, and it's small. They had to keep things from getting out of hand.That is exactly what Disney was thinking when they blocked out most APs at Disneyland for Star Wars Land... and APs waited the 3 months. They regretted that move.
Universal doesn't seem to have a problem changing their mind when needed. It's better to be a little cautious and limit pass holders at first than to have the park over capacity and delivering bad guest experience because a lot of passholders are hanging out because it's new. Passholders are an important part of Universal's clientele, but they make more money of the day guests, and even more off the resort hotel guests. They take precedence.