Maybe because of lack of connection with the world that movie was trying to represent, until now, not many , especially general public understood what the film is all about. The trailer seem like suggest inversion, but again that is big word that people can't relate
At least time travel was familiar enough to audience but the trailer outrightly said no.
Also, the lack of big star certainly isn't helping. John David Washington is hardly a household name like w.smith, michale b Jordan or even jammie foxx or morgan freeman....