the lights fail because they are not designed properly, and are built with poor quality materials. Piaa lights are a total joke, they are overpriced Pilot lights. Why pay $200 for fog lights when they are total crap? I guess its all a marketing thing. Pilot fog/driving lights are made from the exact same materials, and most of the lights are identical... only they cost around $20-$60. The only fog lights I recomend are the OEM lights... they're the only ones I see last. They are built with better materials, the reflectors are computer designed and the wirring harness is perfect.
Hopefully the ones you got this time will last you a little longer.
BTW- what car do you have?