This is victim blaming and only reinforces the status quo. The way things are isn't the way things have to be. We can change the rules if we work together. Or we can give up and blame the victims.
You can have Instagram delete that photo when you change your mind, but how about the friend who saw it and saved it, or the already-illegal bot that crawled the site and archived it?
"Changing the rules" can reduce data availability, probably well enough for most purposes, and that's good. But it's simply strictly true that once you publish something, you cannot assure it's unpublished. And everyone should know this and act that way.
Depending on other people to change their actions when you've been victimized ensures that you'll always remain a victim. You can't control what other people do. You can control what you do.
I think it's more pragmatic advice than anything, even if all these websites deleted your data properly there'd be snapshots and pictures and backups around forever.
