My neighbor’s car went through bulbs in one of the rear running lights almost every month. Since only one bulb was affected, we ruled out electrical surges.
The problem was a loose socket. While the bulb had a good electrical contact, it easily moved in socket. A loose connection between the bulb base and the socket can allow the bulb to vibrate more than usual. This is not good for the filament and it can break when the right combination of heating and vibration occur.
After bending the tabs a bit, the bulb fit snug in the socket and it’s been over six months since the last bulb was changed.