Drayton Manor has that kind of price structure, and it's much more reasonable.
£29 for adults, 12+
£15 for 4 - 11
£8.50 for 3 - 4 year olds
Free for under 3s
In fact most other theme parks offer different price structures for different ages, as few 11 unders can access the 'adult' rides due to height restrictions.
You’ve entirely missed the point again. The manner in which the admission fee is divvied up between age groups is the attraction’s choice, because each theme park is different. If you prefer Drayton Manor’s pricing structure, go there instead, as @JaniceWebster suggests.
Their pricing structure works for them. I’m not familiar with Drayton, but their break even may be lower than Chessington’s, and the mix of age groups may be different. Either way, both parks will have worked out what works best for them with ticket pricing and differential pricing for different groups.You, the customer, either like it or lump it.
You want to go to Chessington because it has a sea life centre and a zoo as well as rides. All of those things cost money. How much does it cost to build a massive aquarium? Merlin Entertainments, the parent company of Chessington, spent £94m on new attractions in 2019. They recoup the cost of those investments through ticket prices, which are arranged according to what the operator wants to charge and what people are prepared to pay. If the flat ticket pricing policy wasn’t working, and they weren’t getting visitors, they’d have changed it. That they haven’t rather speaks volumes about who is being unreasonable.
I looked at Merlin’s 2019 annual report and accounts. In 2019 their profit before tax was £133m on a turnover of £1.7 Bn. They will pay £53m of that in corporation tax. They employ loads of people in the parks and provide work for businesses manufacturing and maintaining the rides and other attractions. Nothing in that paragraph says ‘greedy’ to me.