Some users browsers and computers don't work correctly with SSL. It's a small %, but still causes problems for some.
At the time we designed and built the site eBay's own servers did not offer secure login by default. It wasn't until early 2005 from what I can tell.
Since I don't anticipate us changing this in the near future here is the link to our secure sign in page for bookmarking:
https://www.auctionsniper.com/securelogin.aspx