Kinda of a loaded question. Disneyland has offered more and more to their guests through the years: live shows, parades, state-of-the-art rides and technology, daily fireworks, clean and tidy parks, seemless story telling, etc. But all of that does come at a cost. If you visit other non-disney parks they may be cheaper but you don't get that Disney shine or level of service.
Shareholders demand a return on investment. Higher wages mean higher prices!! Simple economics.
Just like at the airport...a bottle of water costs more than at the grocery store. At least, you can leave the park, make your basic purchases, consume them, then go back to the park.
The $4 price of a bottle of water is common amongst theme parks. Disney used to frown on guests bringing their own snacks and water into the park but now you csn do so freely. So if you absolutely need to be frugal you have many options. Plus bringing a bottle and refilling it at any of the many fountains is still another option.
But why to markup the basic things like water bottle?
Its the way of the world.
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