This may be a question for
@lentesta, but I'm playing a bit of devil's advocate here.
Is there some logic to the day by day capacity caps at any given park? I'm guessing that overall park capacity is reduced, but to the average consumer this doesn't compute logically. It's the airline question, why not just fly the plane faster? Well, fuel efficiency is also important.
So bringing this back to Disney, do they have pockets or tiers (sorry for the corporate buzz speak) of attendance where they deliberately cap attendance on a day where it otherwise may dip into a need for additional cast members? They look at mid-September and know that they can reduce operational costs during that time and identify what optimal operational costs would be in that window. That math differs wildly between Christmas and New Years, but so too does the spending.
That brings forth the actual questions, what is the "fuel efficiency" here? It's probably as straight forward as, MK in September will make the same amount of money with 30K guests in the park as it would with 32K guests in the park, then let's cap the capacity at 30K.
This was probably an ultimate goal of Next Gen that they couldn't do with analytics, so they just made a hard line capacity cap at each park.