The buyer protection fee is the most thinly veiled reason for just making more money. I guess they had to think up a reason and this is what they came up with. I think most people see through it though and see it for what it is.
The only reason that makes sense for them holding private sellers money is to make more money whilst it is in their possession. Therefore they want to hold onto it for as long as they can.
That is the 2nd of 3 new changes. Once the 3rd, Simple Delivery, is mandatory and the buyer purchases their postage label direct from ebay, they will make money on every postage label sold.
That's 3 new income streams at the expense of the private seller. Welcome to greedbay.