Not OP, but thanks to IG and similar sites I hear about celebrity things and other pop-culture stuff way more than before. Case in point: This post.
The place I do find more pop-culture stuff like this is in the clickbait ads that are everywhere now, but that's just an entirely new thing.
I don't think it was until 2015 or so that it started getting huge in terms of user base size, and that's when the deluge of low-grade comedy, "IG Models", awful memes, spammers etc. descended upon the site, changing its culture to what we see now.
now, not the same about twitter. twitter is in the news, articles and everywhere. if anything instagram isn't as pervasive as twitter or facebook imo.
I've seen articles where the bulk of the source is twitter "clippings".
That doesn't happen with Facebook or Instagram.