> Why does this cable have all 24 pins when only half of them are connected? The extra pins could help the plug sit more securely in its socket. Another guess: the same factory makes Thunderbolt cables, and it’s cheaper to maintain just one design, even though that means wasted material and effort.

The highest volume manufacturers may be fully integrated. Usually how it works, especially for these relatively low volume no-name brands, is they buy connectors from one vendor, PCBs from another, cables from another, plastic moldings from another, and then assemble them together (which may also be subcontracted). The assembly process doesn't have to be sophisticated: a small warehouse with a few workers with soldering irons and some jigs. Even some medium-volume assemblies like the USB-C front panel cables for major computer case brands are soldered by hand by a handful of workers in a small building.

Almost all of the USB-C connectors which are available off the shelf have all of their pins populated. Pins are very cheap. You need to be moving a whole lot of volume before it makes sense to go to your connector manufacturer and ask for a custom one with missing pins.