Consoles ship as one configuration that cannot be upgraded. The restriction is deliberate, and it produces advantages that a variable specification cannot deliver.
Optimisation requires a known target
A developer writing for one machine knows the exact processor, memory bandwidth and storage speed available. Code can be tuned to those numbers rather than to a range.
That allows techniques a PC version cannot use, such as relying on precise memory layouts or precompiled shaders that assume one graphics architecture.
The result is that console hardware typically outperforms equivalent PC components in games built for it. The gain comes from certainty, not from the silicon.
The business model depends on a single unit
Console hardware is often sold at or below cost, with the platform holder recovering the difference through software royalties and store revenue.
That only works if buyers of the cheap hardware go on to buy software on the platform. A single specification keeps the population and the software library aligned.
Upgradeable hardware would fragment that population and make the subsidy harder to justify, because a machine could be bought and used differently.
Certification depends on predictable behaviour
Platform holders test every release against performance and stability requirements. Those tests are meaningful because the test hardware matches every player's hardware.
A variable specification would make certification probabilistic, and a game passing on one configuration could fail on another.
The guarantee that a purchased game runs is a large part of what the platform sells. It is enforceable only against a fixed target.
Mid-generation revisions strain the model
Enhanced consoles released partway through a generation introduce a second target, and developers must support both. The advantage of a single specification is partly given up.
Platform holders manage this by requiring that games run on the base machine, treating the enhanced version as an option rather than a separate platform.
This keeps the library unified but caps ambition at the older hardware, which is why enhanced modes deliver resolution and frame rate rather than different content.
Fixed hardware ages in a specific way
Early titles rarely represent what a console can do. Developers learn the machine over years, and late-generation games extract far more from identical parts.
A PC never sees that effect, because the target keeps moving and effort goes into breadth of support rather than depth on one device.
The trade is therefore between a machine that improves through software and one that improves through purchases. Both are coherent, and they suit different buyers.