Adding storage or memory at the point of ordering a device costs several times what the same components cost separately. The pricing follows from when the choice is made.
The decision comes after the commitment
A buyer configuring a machine has already chosen the model, compared it against alternatives and decided to purchase. The upgrade question arrives after that.
At that point the comparison is no longer between competing products but between two versions of the same one, and the alternative to paying is accepting less.
Price sensitivity is much lower in that position, which is precisely why the upgrade is presented at that step rather than in the headline price.
Why the base configuration exists
The entry configuration sets the advertised price, and that figure is what appears in comparisons, advertisements and search results.
Keeping it as low as possible matters commercially, even if relatively few buyers ultimately choose the specification it describes.
The base model is therefore built to a price rather than to a sensible balance, which is why its storage often looks inadequate for the machine's capability.
The role of soldered components
Memory and storage were once replaceable, so a buyer could take the base model and upgrade later at component prices.
Soldering them to the board removes that option, and the technical justifications of thinness, power and speed coexist with a clear commercial effect.
Where components remain replaceable, upgrade pricing from the manufacturer tends to be more restrained, because an alternative route exists.
What the upgrade actually costs the maker
Memory and storage are commodity components with published market prices that fall over time and are bought in enormous volumes.
The difference between a manufacturer's upgrade price and the component cost is one of the highest-margin transactions in consumer hardware.
This is not hidden. It is simply presented as a product tier rather than as a component price, which discourages the comparison from being made.
How to approach the decision
Storage that can be extended externally is worth less at the point of purchase than memory, which usually cannot be added afterwards at all.
Where internal expansion is possible, buying the base configuration and upgrading separately is generally far cheaper, though it may affect warranty terms.
The question worth answering is which constraint would bind first over the device's life, since paying for the wrong one is the expensive mistake.