What eBay is trying to do is protect themselves from the allegation that they are flagging accounts so that they can profit from the interest on the float. The

What eBay is trying to do is protect themselves from the allegation that they are flagging accounts so that they can profit from the interest on the float. The easiest and cheapest way to do that - for them - is to simply hold the float in a non-interest bearing account. By contrast, giving the interest to the sellers would add a lot of paperwork and complications relating to taxes and such.