Air conditioner compressors usually fail due to one of two conditions: time and hours of operation (wear out), or abuse. There are some failures that can occur elsewhere in the system that will cause a compressor failure, but these are less common unless the system has been substantially abused.
Usually abuse is a result of extended running with improper freon charge, or as a consequence of improper service along the way. This improper service can include overcharging, undercharging, installing the wrong starter capacitor as a replacement, removing (rather than repairing/replacing) the thermal limiter, insufficient oil, mixing incompatible oil types, or wrong oil, installing the compressor on a system that had a major burnout without taking proper steps to remove the acid from the system, installing the wrong compressor (too small) for the system, or installing a new compressor on a system that had some other failure that was never diagnosed.