I ran two Focuses a 2004 Zetec wagon 183,000 miles and a 2000 SPI sedan for ~ 50,000 miles.
Not one headlight was ever replaced
You have an electrical issue
Get yourself a multimeter
Go to YouTube
Type in battery, alternator, multimeter
There you will find a multitude of 'How to' videos of varying quality
Now having said this I suppose if you drove at night alot and went over pot holes, speed bumps and the like that MIGHT make a difference. I would imagine your front end would have disintegrated by now.
How does the connector going on the head light look, if it is all burned up [bad connection] then the heat generated by a bad connection could make a head light fail earlier