I also search in multiple languages but I also know that's an exception. The majority of the people in the world likely would only use a single language and it's easy to believe that search results are better for those users with languages separated.
There are cases when I'd even like REGION agnostic results, or least ones not bound by national boundaries. For example, I have an interest in my state history (MI), and there's plenty of relevant articles/commentary from the Canadians.
A Canadian/Indian/EU-based Google probably would've ended up with multi-lingual support, whereas a China/UK based one probably wouldn't have.
By the time Google got big enough for international considerations, there were already a bunch of baked in assumptions about their users, like them being monolingual.
Hell, I'd love to have the option to make the search results be completely language agnostic.