Flight Coupons

I don't normally post over here, but I recently took the Shuttle several times. Why doesn't US staple the flight coupon for paper tickets onto the back of your boarding pass? Every flight I boarded there was at least one person with a paper ticket who only handed the gate agent their BP without the flight coupon. The gate agent then scolded the passenger and said s/he couldn't board without the flight coupon. It seems quite odd that US doesn't attach the flight coupon in any way, as every other airline does. I also find it odd that US doesn't collect your BP if you have a flight coupon, but I guess that doesn't really matter. Is this because check-in agents are being lazy and not stapling the coupon to the BP, or does US have a policy against this? It seems so odd, since it always slows boarding as the passenger looks for their flight coupon.