Strange decision. The AI overview won't disappear but the UK news publishers will disappear from it. People who use a news publisher usually open their websites, not Google. People who open Google to look for news mostly are fulfilled by the AI overview content, if it isn't, they always can check links below the AI overview.
Correct, the click through from AI Overview is better than nothing, but it's not typically (anywhere near as) high as it would have been if the website was shown in the results without AI Overview at all.
Furthermore, opting out of AI Overview means that _other_ websites will be used for its grounding. Those competing websites will be cited and receive some citation traffic instead. So there's really very little incentive to opt-out for most websites.