I suppose they have to strike a balance. On the one hand they have to create a market place where sellers feel safe and secure. An auction site without traffic is dead, hence the reason why most other auction sites fail. Ebay has the traffic and is trying to ensure that it keeps it.
Make the buyer feel secure and they will come to the site. In my opinion though, ebay has tipped too far to the buyer side and ignored the sellers. The decision to stop sellers leaving negative feedback is one example of over protecting the buyers at the expense of the sellers.
Perhaps ebay thinks as long as it can keep the buyers happy and generate lots of traffic the sellers will always be there, even if some leave others will replace them. And maybe they're right. Most sellers will ride the blows ebay hits them with and keep coming back as long as there is traffic to sell to.
There has to come a point though, when many sellers will say enough is enough. That point will come when sellers can't realise their profit margins. Operating on ebay takes time and effort like runing any business, if you don't see the returns you will eventually say it's not worth it.