alt Hacker NewsIt reduces the value of their ads.
Let's say you are an ad buyer. Previously 1M clicks resulted in 1000 sales, now 2M clicks result in the same 1000 sales. If you previously paid $1000 for 1M clicks, you paid $1/sale. If they are now asking you to pay the same $1000 / M clicks you'd be paying $2/sale, so Google would have to drop to $500 / M clicks to offer the same value to advertisers.
But the same applies to ad sellers as well. Google would have to slash payouts to websites displaying ads by the same 50% / click or they'd be cutting into their margins. A competing ad platform without fraudulent clicks would be able to slide into this space, offering both a better value to ad buyers and a better payout to ad sellers, so they'd be taking market share from Google without having to do anything themselves.
Of course that assumes a market in which the value of ad clicks, views, and placements is clear to everyone and switching between ad platforms is trivial, which is not even remotely the case.
Sure but for the ad network, it means they can brag to new clients about how many clicks they can get them. If the ad clicker isn't buying, that's the client's problem, you already did your job by getting them to click. Maybe the client needs a more direct campaign (which costs more) or needs to change their website/prices, people are walking into the store but they just aren't buying.
Its either the ad network running these click botnets or contracting someone to do it. If it was just impressions getting boosted, that just looks shady, those are barely worth anything.