it's done to make eBay a profit
And this also has an affect to stop people from wasting everyone's time and their server space by listing products at prices that won't sell.
Also, a little bit of trivial data I collected over the last week as I was trying to sell a player of mine. I was looking at players of similar skills on the transfer market (I'm talking about the upper end players that cost 1 mill+) and I noticed that the clearance rate of these similar players is around 10-15%. So that means for every 10 players transfer listed, only 1 will actually satisfy both buyer and seller's prices.
The majority of prices listed at is way too unrealistic like a 30% surcharge on what the player realistically is worth. These same players just keep coming back up on the transfer list.
If you are a true believer of an efficient market theory then by right if you list a player for $1, then the market will drive his price up to what he is actually worth at that point in time (which takes into account time listed and skills).