The problem is merlin have already made it clear many pass holders are pre booking and not turning up, increasing pass holders tickets makes this problem worse and I can see why they don’t want to give pass holders too much % of the capacity they have for them not to turn up.
They could introduce a higher pre book price (seems unlikely now they’ve made it free) which gives you money back when your at the park to spend.
Or you could have some sort of system which gives gives priority to Those who have actually turned up and gone instead of booking and not going, problem
with both options is I doubt they have the systems in place to do anything like that.