No particular reason. I'm not sure how much more smoky they would have tasted with one more load of chips. Three hours of smoke left them plenty smoky, definitely not "mild".
Back to the original post - any reason you waited 45 minutes to put in the chips for smoke? I usually try to get the smoke rolling BEFORE I put the meat in so that it's always exposed to smoke while in the smoker. Was it for just a mild smokey touch?