They don’t, if they did they would remove such content immediately, they definitely do have the resources to do it as big companies. It’s why IG, FB etc. have content moderators that work to not approve this types of posts, but their conditions aren’t very good from the documentaries that are made and there’s too less of them to remove this kind of content (and other more vile content).

Instagram unfortunately only has a one goal: making money and having engaged users with the platform and spending time on said platform. The fact that these were shown in the user’s algorithms even though they previously haven’t watched such content, simply because it was popular just goes to show where their interest lies despite instagram also having underaged/teenagers users exposed to such content.