Perhaps I can explain with an example from a buyer's point of view. Let's say I buy Chip A on Ebay. The bidding was heavy but I manage to win the item by outbidding the second highest bidder by $1 and the second-highest bidder by $2. Now I buy Chip B. It's listed on Ebay with a minimum bid and a secret reserve. I bid on Chip B but don't meet the reserve. No one else bids. The seller contacts me and offers me the item for price C. I buy it. Later I want or need to sell chips A and B. On Chip A I can probably be confident I can get at least close to what I paid by reselling it on ebay. On Chip B I have no idea. All I know is when it was offered on Ebay NO ONE bid except me bid.
Can you see why I as a buyer would rather buy in an open auction rather than buying later privately from someone who was selling with a secret reserve?