Peak Season Airfare

I was checking airfare from LAX to CTU on Cathay Pacific's website for this September. If I travel during the week of the 15th, round-trip airfare will be ~$2400. If I travel a week later, then the price drops to ~$1200. Other than an arbitrary definition of "peak" season, nothing changes from one week to another to warrant a 50% price drop. I also didn't expect the difference to be so much... I wonder if they have any passengers during the last week of peak season.