Because they serve their own independent search index. Others, under the hood, just use Bing or Google API for searches. This could mean that searching on other engines queries the sites that enable abuse described in the original article. Other sites that operate their own index include Yandex but because it's headquartered in Moscow, Russia, I have doubts about their privacy. This is what leads me to conclude that Brave Search has the best general privacy. I'm not entirely convinced by DuckDuckGo because it could just be a honeypot since it's approved by Big Tech gatekeepers.