Sniping is done is the last few seconds, there's only one chance. Nobody 'keeps sniping', you have one shot to bid the max you are willing to pay, and everyone does it at the same time. Whoever is willing to pay the most wins, and we don't get to see their 'hand' first.
It's highest hand wins, without newbie or shill bidders calling bluffs.
Sniping is necessary because there's idiots out there that need to be 'winning ' the auction even if there's days left.
ie you bid $30 max, current bid $5
newbie1 $6
newbie1 $7
newbie1 $8
newbie1 $9
newbie1 $10
newbie1 $11
newbie2 $12
newbie2 $13
newbie2 $14
newbie2 $15
newbie1 $16
newbie3 $18
etc etc
the same few idiots fighting it out trying to be the top bidder and catch up to whathever your maximum is, days before the auction is due to end, but doing it in the minimum increments because they want to beat you by the bare minimum, not just chuck down $40 or something.
There's days left, but they are probing and probing, keeping upping the bid be the smallest increments to try be "winning". Add more insistent newbies and a higher number of them, your $30 is worthless,. It just decided the minimum price this item will sell for, that's all.
If you didn't set a bid for $30 in the beginning, these other people might be sitting on $15-20, then you'd snipe their arses and get it for $21. Edit unless someone sniped higher. But fair enough, they were just willing to pay more than you,* they didn't play silly games beating you by 10c, or in slow motion bit by bit trying to take it for as little as possible.
* I differentiate willing to pay more than you (ie. sniping) to willing to beat you in small bids (ie idiots with a competitive streak that will pay whatever it takes slowly but surely just to 'win' something, not matter what it costs, they get lost in the bidding war - not to mention it leave you open to shill bidders). They can retract their bid after they know what your max bid was as well after working it out when they start 'winning'.