Why do Air Conditioner capacitors go bad now and then?!

There are many reasons for that. I mention some of the most important ones in brief:

1- Voltage spike or fluctuation.

2- Old or defective compressor.

3- High ambient temperature.

4- Dirty condenser coil (result in the compressor draws more amperage than normal)

5- Any blockage in the system

6- Dirty capacitor

7-Ending the lifespan of the capacitor.

8- Thermostat or ambient temperature sensor in Indoor Unit goes bad

9- Compressor oil acidity.