I'm honestly not trying to be mean, but I'm not sure you understand human psychology in this area. Humans are very consistently swayed by looks over intrinsic value.
People aren't necessarily doing quantitative A/B tests between search engines, they're just plugging the latest search terms they want answers to into the search field and (in many cases) getting a search result that seems to fit the bill.
If the search engine displays results in an visually uncluttered (seemingly authoritative) way then that would seem like a good search engine choice.
There was that blog post the other day where someone updated and improved their site design and was lauded by users for all the new features they had introduced, when all they'd done was refresh the design.