I think that has to do with the marketing and all the memes about how much "less" of the film you see if not watching it on 70mm IMAX
Which is true. He didn't shoot in 35mm so if you want to get the full shot on the screen you must go to an IMAX theater.
1.43 IMAX isn't exclusive to 15/70mm, it can also be screened with IMAX's dual laser projection system.