First, certain materials (usually the cheap ones) age much faster than others. This affects rubber domes (even in Topre with otherwise capacitive switches) and ABS (yellowing, poor resistence to sweat and other abuse) for the most part. Besides, the keyboard may still work after years, but what about comfort/feel?
Second, it always depends on the assembly quality. You can have a mechanical keyboard with ****ty soldering on the PCB or a loose cable connection (like the rosewill mentioned above). The good thing is that some mechanical keyboards are kinda modular and it's quite easy to find replacement parts.
At last but not least, use case, environment and user's behavior are a big deal. A clumsy, messy idiot can destroy any keyboard in no time. Dust, pets, rage, spills, using the keyboard as an ashtray, you name it.