Why was the multi image technique abandoned?

Indeed, the more standard split-screen employed in Pillow Talk is almost as old as talking pictures and, since their advent, was used almost exclusively for telephone conversations, to the best of my recollection. Or, in the case of a film like Airport, for radio communication with aircraft. My recollection, of course, is by no means definitive. Pillow Talk brought some wit to the device; notice, below, how Day is framed in a deliberately intrusive triangle between Hudson and his amour du jour.



And earlier still, Abel Gance employed multiple images in 1927's Napoleon.