A few days ago I told my wife that Instagram was owned by Facebook and she was shocked. She had no idea. There are clues scattered around, mostly related to trying to get you to add your Facebook friends on Instagram or trying to get you to use Instagram more but not much else. I couldn't even find the word Facebook on Instagram's site just now (not even on their About Us page). It's probably on there somewhere but it seems to be pretty deliberately disassociated with Facebook.

I wonder if Facebook is treating Instagram like a second earth. If they ruin the first they still have a backup.

Both are acquisitions.

Not only are both acquisitions, but Facebook's strategy there might also involve diversification and disassociation with the parent brand. In other words, they foresaw they'd take a hit in user trust and even popularity so they're OK with spinning off new features as a completely different brand. The negative perceptions Facebook is currently dealing with don't really bleed into (at least in the minds of users) WhatsApp and Instagram, even though they now are part of the same engineering culture.