Apple does a great job of fitting components in its devices. But these components are not always the best. Since the Apple devices themselves are created before they are shown to us. And Chinese and Korean companies do not let new products lie down and immediately throw them on the market.
Why? Apple is an ideal scheme - they are selling not a technical device, but an "image". Appearance. If you look at the history of the creation of the Apple Company, you can understand that, in principle, they did not do anything revolutionary - they simply sold "prestige" to the office plankton. So it just makes no sense for them to invent something very innovative there
Apple products are bought anyway. A larger battery costs more, which means less will fall into Apple's pocket from each phone. And the overwhelming majority of Apple users do not ask this question at all, they are stupidly sure that Apple has everything the best, including the battery. Not like "some Huawei or Xiaomi".