Inventory.

Insta was tapping out of how much content (and therefore ads) they could show a user. They could either find new content to show or add more ads per unit of content. There are only so many friends, who only take so many photos. Social media stopped being “social” because it just wasn’t as good of a business as generic media. There are endless influencers and videos is way more engaging. Influencer content is semi-professional content and is way better made and way more engaging than your family who posts only at big events. Meta is very data driven, and they understand exactly how reels is increasing duration of app sessions - which means more ads.