A broken device is often physically repairable and commercially unrepairable at the same time. The gap between those two states is created by supply rather than by engineering.
Parts availability is a business decision
Manufacturers order service parts in quantities forecast from expected failure rates, and that production usually ends when the model leaves the market.
Once the service stock is exhausted, a repair depends on salvaged components or third-party equivalents, both of which are inconsistent in quality and supply.
The length of that parts window varies enormously by category and manufacturer, and it is rarely stated at the point of sale.
Assembly choices set the labor cost
Adhesive, soldered components and modules that combine several parts into one unit each raise the cost and risk of a repair even when parts exist.
Where a common failure sits inside a large assembly, the replacement part carries most of the device's value, and repair stops making economic sense.
These choices are usually made for thinness, water resistance or manufacturing cost rather than to prevent repair, but the effect on repairability is the same.
Software gates are the newer constraint
Many devices verify that a replacement component is the one originally paired with the unit, and refuse full functionality when it is not.
Pairing tools generally sit with authorized service providers, which means a technically correct repair can still leave a device partly disabled.
Diagnostic software carries the same problem, since identifying the failed component may require access an independent shop does not have.
Right to repair rules are changing access
Several US states have enacted laws requiring manufacturers to make parts, tools and documentation available to independent repairers on commercially reasonable terms.
Coverage differs by state and by product category, and exclusions for certain equipment types are common, so the practical effect varies by where a device is serviced.
Some manufacturers have responded with self-service programs offering parts and manuals directly, which improves availability without necessarily improving price.
Repair cost is measured against replacement
A repair competes with the current price of a new equivalent, and falling prices in a category quietly shrink the range of repairs worth performing.
This is why repair remains routine for appliances and vehicles, where replacement is expensive, and rare for small electronics, where it is not.
The determining factor is therefore the relationship between parts pricing and new product pricing, and manufacturers influence both.