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.