A mechanical switch is a tiny precision mechanism, four parts that decide everything. A two-part housing (top and bottom, in nylon, polycarbonate or POM blends that set the sound and the feel), a cross-shaped stem the keycap clips onto, a weighted stainless spring rated in grams-force, and metal leaf contacts that close the circuit. The geometry of stem and leaf sets the character: linear (smooth), tactile (a bump) or clicky.
The reference design is one shape: the Cherry MX cross-stem. Cherry's MX patent eventually lapsed, and that single fact created this whole industry. Once the mount was free, the Dongguan and Huizhou makers cloned it, and every switch since is MX-compatible, which is why a keycap from anywhere fits a switch from anywhere. Nobody competes on the mount. They compete on plastics blends, tolerances (stem wobble), spring tuning, factory pre-lube, and hot-swap 3- or 5-pin versus solder.
This is the rebadge in its purest form. Enthusiast vendors, NovelKeys, Glorious, Akko, Drop, Keychron, Zeal PC, commission custom switches, choosing the housing material, the stem, the spring weight, the colour and the lube, and the factory makes them. Gateron built the Zealios line for Zeal PC and makes Keychron's house switches; the name on the switch is often just the buyer. The same linear can ship under five vendor names in five housing colours.
The live frontier is the magnetic, Hall-effect (analog) switch for rapid-trigger gaming, adjustable actuation in the Wooting mould, now made by Gateron, Outemu, Kailh and TTC alike. Lifecycles are rated at 50 to 100 million presses on force gauges, and the better houses run German injection machines and Swiss CNC. Above this layer sit the parts you cannot hire: Cherry in Germany, and the keyboard brands (Logitech, Razer, Keychron) themselves.