I assume that ebay started charging FVF on postage because, years ago, some unscrupulous sellers would try to reduce their FVF's by offering a £10 product for sale at £1 with £9 postage. Probably not the best solution for sellers or buyers, but it certainly resulted in millions of pounds of extra profit for ebay.
Now FVF on postage is one thing, but why is ebay now charging the sponsored listing fees on postage on top of the FVF?
Sellers generally don't make profit on postage because buyers are aware of postage costs and will simply go elsewhere if sellers overcharge. Unfortunately, we already have to inflate postage costs by up to 15% to account for the FVF's that ebay are charging on them. Now, on some sponsored listings, we have to charge £2-£3 more that the actual postage cost just to break even on it after ebay take all the fees off!
I doubt that buyers would be impressed if it was common knowledge that of the money they just paid for a guaranteed next day service, ebay were taking £2 - £3 of it for themselves with no benefit to anyone else.
Is there a valid reason for this policy change other than increasing ebay revenue?