Well, for me not a matter of realization, but a matter of logic. You use your pants more than your jacket. Each time you get up from your chair you are scuffing the fabric. The threads will eventually wear, and as you've experienced, occur much faster than your jacket. The pants are not hung whilst you are working; they are on you from the moment you put them on to the moment you take them off, which is considerably longer than when your jacket is on.