Well stainless steel is like all engineering, a compromise.
So you exchange one set of properties for something else. Certain stainless steels can remain stainless in more benign settings, but in harsher settings may corrode slightly. or a process like welding can alter the properties around that area etc.
Truly corrosion proof stainless steels tend to be less strong, or they're horrible to machine etc. etc.
Regardless of this, it's a still a lot easier to maintain and keep nice than plated steel.
