Why are sellers prevented from leaving negative feedback for buyers who fail to pay

[royalsfragrances]

Why are sellers prevented from leaving negative feedback for buyers who fail to pay for items and who don't respond to emails?

I know there is a Report A Buyer option but negative feedback alerts other sellers that a bidder can be a potential time waster and therefore enable the seller to decide if they wish to cancel a bid on their items?

In the last 2 weeks I have had 2 non paying bidders, one of them I have since checked their 10 positive feedbacks only to find that negative comments for non payment and for non response to emails make up 3 of the 10 feedbacks however the sellers who have left the negative comments have had to do so under the 'Positive' comment option.

At this rate such a poor seller will never be prevented from using eBay and many other trustworthy sellers will possibly lose out on sales and have lots of time wasted sorting it out.