I'm assuming you haven't followed many ebay auctions? It's very rare that an early bid ever wins unless it's over the odds or the only bid. To have a good chance of winning you need to bid at the end - most users know that. Auctions that finish at the wrong time (like the middle of the night) usually achieve a lower price.
If everyone uses a sniper it effectively becomes a sealed bid process and in those circumstances you'd be pretty silly to reveal your bid before you need to as you're telling everyone else what they need to bid to beat you.
You're assuming that no one will increase their maximum bid if they realised that someone else has bid higher. Like I said it's the psychology of auctions - in the heat of the moment some bidders will go above their original limit to win the item. After you reveal your bid someone may outdid you by a very small increment just to beat you and it may be too late for you to react.
If everyone used a sniper final auction prices may be lower in the long run. And it's much more convenient to use a sniper anyway as it does all the work for you.