Because the neg would also be accompanied by a NPB strike, and three strikes and that buyer's OUT. It would also help sellers evaluate offers from that person--for instance, if I had a bag that I was selling and I got two very similar offers, and was deciding which to decline and which to accept, a few negs would certainly steer me away from little miss my kid did it.
Oh, and you can also block bidders who have received two strikes in the last 30 or 60 days or whatever it is.
Last point: feedback is supposed to be *accurate*. In this case, the seller's experience with that buyer WAS negative. I think that it's important to leave accurate feedback, personally...though I realize that many sellers are very hesitant to leave negs. I personally do not fear the neg. I wear the few I have (in approx 1300 transactions) with pride.
ahhh - I din't think about the offer thing