This just isn’t so.
'Cause I like to build spreadsheets, I built one containing all B. Picture nominees since 1927 (476 of them, not counting this year) and researched every single film’s box office takes*, ranking them both in the overall population of movies released that year and within the subset of B. Picture nominees for that year.
The results are pretty conclusive: Box office success is a large, if not the largest, predicator of which movie will win Best Picture:
… 27% of Best Picture winners (22 films out of 82 awards) were the #1 box office grossing movie of the year upon initial release (caveat: in three of these years (61, 46, 40) the B. Picture winner was overtaken by a Disney film with multiple releases in subsequent years. All my sources combined the release #s for Disney movies.)
… 77% of BP winners were among their years top-10 grossing films. The first Best Picture winner not to be a top-10 film was 1948’s Hamlet, which ranked 17th in box office. The first BP winner not to be a top-20 film was 1987’s The Last Emperor (#25 for the year).
… The average yearly box office rank of BP winners is 8.5. For losers it’s 19.27.
… Within the categories themselves, if you rank the nominees by box office grosses, there is a 41% chance that the highest grossing movie will win the award. For the top-two highest grossing movies, there is a 71% chance of one of those winning. Only three movies ranked last among grosses won the award - oddly enough, all in the late 1940’s.
You have a yearly award that is open to approximately 120-400 movies per year (depending upon # of films released) and the statistics show that 27% of those already awarded just happen to have gone to the most popular movie of their year, and 77% of the statues have gone to films that were one of the 10 most popular of their year.
This is not a coincidence.
I stand by my statement - Best Picture is an industry award given to executives who were successful in guiding film projects through to completion and, ultimately, audience acceptance and financial reward. It is not an award based on the artistic merits of the film - that’s what all the other awards are for.
*Mostly Wiki and BoxOfficeMojo.