Cause he wants to do the chicken dance at 147. He wants to do it at as many divisions as possible. Zab Judah, the 5 weightclass chicken dancer. On a serious note, its all in the opponents. If he want to 140, most of his fights would have to be in Europe.
real simple answer - money. He is making more now, even though he is losing, than he ever will if he were to dominate the junior welter division. I mean, the guy has an upcoming ppv with shane mosley and you ask why doenst he go to 140? cmon man