I can't imagine it came from Instagram having a shortage of content.
e: Like, the quality and relevance of the content is the main value proposition to users in an old school social network like Instagram. You can't really mess with that in service of some other goal without undermining the product's raison d'etre.
So why would they do this? Is it just another attempt at swaying public opinion (see: Cambridge Analytica)? Perhaps promoted messaging will come from these accounts so they can monetize their AI investment? Whatever it is, it doesn't seem like a feature users requested so it's difficult to think it benefits them.
Facebook, like Google, is a surveillance advertising company that tricks you into using their products so you provide targeted ad information to them. They know when or if you poop regularly l, and what brand of TP you use. Your AI friends will help them advertise better.