Sure! Facebook makes more money managing private information than virtually any other company. What's the larger company they'd need to deter?

Every single company that collects, stores and uses any personally identifiable information should be deterred from abusing their privilege of doing so.

Yes, and how does a $5B fine not accomplish that? It's not like any smaller company can look at this and say "well, the total valuation of all firms pursuing these activities is larger than the fine, so it's rational to continue doing that". By all means, fine every company that does this $5B, though.

It may deter smaller firms. It's won't deter Facebook.

Why won't a $5B fine deter Facebook? That's a huge amount of money, even to Facebook. More importantly: it is almost surely a giant multiple of the revenue Facebook obtained from the specific behavior that violated the consent decree.