I don’t know much about the recommendation algorithms used at Pinterest or Instagram but in my experience they aren’t very good. I think the reason why is that they don’t know why I like something. Something complicated and full of detail, like a picture, has too many factors at play to know why someone likes it.
Show me a picture of a front entry to a house with clean lines and reclaimed wood furniture. I’ll indicate I like it, but Pinterest has no idea that it is simply because of the light and the feel of it. But someone else might indicate they like it for a completely different reason. I don’t know how the algorithms handle this today, but they have a lot of room for improvement.