Manufacturers could make the storage for larger devices like they do phones but it would be more expensive and no added benefits (there’s always an exception to the rule).
Manufacturers could make the storage for smaller devices like they do desktops and laptops but it would make the end product way bulkier and the market doesn’t want bricks, phones are plenty big as they are now.
Also, even though the internal components are larger, modern desktop storage like SSDs are often sold in a case much bigger than the internals to maintain compatibility with storage slots on computer cases and laptop shells.
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