The cause is that the buyer's query is being answered inside the AI panel before they ever reach the site. What ChatGPT shows, what Claude shows, what Perplexity shows, and what Google now stacks above your blue link as an AI Overview: those are the surfaces buyers read in 2026. Position 4 still holds. The click that used to come with position 4 does not.
The lift is going to whichever sources the AI panel cites by name. The AI panel cites pages that are structured for it to read. Most SEO consultants are still running the 2018 playbook: more content, more keywords, more rank-tracking dashboards. That playbook addresses the wrong surface. Your competitor isn't running more SEO. Your competitor is being cited inside the answer.
The fix is a different discipline. AEO: the discipline of getting cited inside ChatGPT, Claude, Gemini, and Perplexity answer panels; and GEO: the work that surfaces your pages inside Google AI Overviews, are two distinct work streams.