I'm very familiar with the best picture winners. The only qualification is that the members voted for it. And the members are creatives in the film industry who either have already won an Oscar for something like best actor or best director or who have been sponsored by multiple other members for membership.

So those members clearly recognized or connected to something in the movie that has merit to vote for it for best picture. I think it was the fact that it was both unique and surreal but also accessible with an emotional core. Personally, I'd rather see more films that take chances like that than traditional "Oscar bait" (most of which I also enjoy).