Tl; dr - a mix of value engineering and consumer preference. You wanna buy a $3k TV, or a $700 TV? How rock solid does your automatic sprinkler really need to be, compared to a satellite radio in the Sahel?
Per IPC industry standards, there’s three classes of electronic workmanship/quality control used:
Class 1: It works, just about. Shoddy soldering is okay as long as connectivity is maintained. Passing a QA test may be as simple as “it runs when powered”. This is where most consumer grade stuff lives: calculators, watches, flashlights, etc.
Class 2: Better built with generally more QA. Testing usually involves actually checking for function and different modes. Generally used only on commercial/civil government stuff like traffic lights, power controllers, heavy machinery - anywhere where reliability and longevity is worth paying more for.
Class 3: Complete process control and 100% coverage function (and almost always) burn-in/stress test cycles. Top quality and cost, typically only used for military, aerospace, or medical - where stuff failing means people die.