It's a rather easy answer to say that ebay simply loves bidding wars. To me, anyway, it is obvious only that ebay would, all else being equal, dislike a sniping function to be available to the bidders in each particular case in which there is a bidding war. However, I'm thinking in terms of the enterprise as a whole, not isolated cases in which there is in fact a bidding war. Like I said, it's not clear to me that the more people learn of and resort to sniping, the less the final auction prices in the aggregate for all items as a whole, or the less ebay's profits overall. Remember that people who know in the first place what the point of sniping is would have AS or some other sniper service to resort to anyway. Even if there were a concern that sniping could suppress bidding (which isn't clear to me, speaking in the aggregate), ebay can be discreet about its own snipe function if it chooses, not actively advertise it, etc. Also, for example, eventually a snipe function could result in a greater number of bidding participants. And so on. If you think about it, I think it's a bit more complex than ebay just preferring a bidding war (all else being equal--but all else is not necessarily equal).
So again, it is not clear to me that ebay would not gain substantially from adding a sniping function, even regardless of whether not they could earn anything in the way of fees from such a function. And adding the function can't be a big deal for a company with ebay's resources.