Here's the insides of one model Eric Hendrickson calls a "Plastic Pentax" :
Just look at all those plastic gears!
The Pentax ZX/MZ series Achilles heel is a plastic gear in a critical place.
Once it breaks - and it invariably does - camera is completely disabled.
The replacement motor came with a metal gear, but it requires complete disassembly
and it is now no longer available.
IIRC some of the Minolta X-series cameras have a plastic gear that often breaks, disabling the camera.
No doubt countless other later model film SLRs from all manufacturers were built similarly.
Cheap now yes, but I consider them disposable cameras.