Brake calipers are simple devices. The cylinder has a piston, rubber o-ring and a boot. The only moving part is the piston. Motion is caused by either hydraulic pressure, or the o-ring, which deforms when the piston is pushed in by the brake fluid. After the pressure is released, the o-ring returns into the original position and pulls the cylinder from pushing on the brake pads. When the brake pad wears enough, the piston will push further through the o-ring, and automatically adjusts the brake. The boot only keeps dust and water from the internal assembly.
The only problem that can occur with this system is contamination. Either corrosion, or particles can jam the piston, due to the tight tolerances. At that time, the caliper can be repaired, or replaced...or that's what used to be the solution.
You can't buy rebuild kits for calipers at parts houses, so you have to buy a rebuilt caliper, pay more, and spend more time returning the old calipers as a core. It's a win-win for parts houses, rebuilders, and attorneys. To me, it's silly crap, and it irritates me something so simple is corrupted by greed and stupidity. .