That's called the tragedy of the commons, everything starts pure and innocent, that's why people tend to romanticize the "early days" before X

They certainly have moderation now, and it's a constant exercise in boundary-pushing. I'd be interested in a "history of Instagram moderation", that would be a great piece of anthropology.

Was the no-links policy there from the start? I think that would have helped a lot. As it is, you're allowed basically one outbound link from your profile, so there are link-expander services which people use to link to more things.