Luck of the draw I guess.
There can be a myriad of reasons. Low profile tyres, rough roads of Karachi, constant riding on those drainage holes all across DHA, weather, driving habit, I once bought Nestle milk instead of Olpars etc. etc.
No car is same neither is its usage the same. I've seen cars lose their transmissions in 30k whereas others go 200k. So many factors come into play that its difficult to pinpoint as to why one wear item is consumed faster than others. But unfortunately wear items do exactly that, wear out.
So far car hasnt suffered any catastrophic failure, so its ok. It is 16 years old after all