Why do people click the ads on search arbitrage pages?
Because the ads often match what the person wanted. A good arbitrage campaign attracts someone already curious about a topic, say hearing aids, then offers searches and sponsored results about exactly that. The visitor is choosing between sellers, much as on a normal search results page. Clicks driven by confusion or trickery exist too, and those are what policies target.
The healthy case rests on search intent. The creative sets an honest expectation, the content page informs, and the sponsored listings are the natural next step. Advertisers get a prospect, and conversions follow.
The unhealthy case uses clickbait, a misleading ad or implied functionality, for example an ad that looks like a button to claim a benefit. People click because they think the result is the thing they were promised. Those clicks do not convert, the search engine detects it through conversion data, and the publisher pays through smart pricing or a clawback.