Simple answer to your question - because they like to make as much work as possible for sellers. I feel like I've reinvented the wheel a dozen times or so in the last three or four years on ebay. I just finish one lot of editing and they change something else and I have to do it all over again. I could better spend my time doing more listings!

I was doing them singly until I re-read a friend's email and the penny dropped about still being able to do them in bulk from the Unsold section on the All Selling page. It's still a pain but it's a whole lot better than doing them one at a time!!