School holidays are the market. Demand appears in defined weeks, from parents searching for something to do with children who are already bored, and the parks that ranked in advance take the whole of it.
School trips run on a completely different clock. Teachers plan a term or two ahead, they search for curriculum links and logistics rather than fun, and the same school returns annually once it has been.
Age is the filter that matters. Something for a six-year-old and something for a group of fifteen-year-olds are different searches, and a park that names the ages it suits gets the right families and avoids the wrong ones.
Weather-driven searches arrive with almost no notice. A dry spell in a wet fortnight produces a surge of people looking for something outdoors today, and a page that already answers it takes those bookings within the hour.