Earlier quoted context omitted.
I have multiple Facebook accounts (I created them for testing a long time ago). I use only 1 of them. But it's funny to see Facebook claiming that Account #2 sent a "friend request" to Account #3. And offering up the other accounts as "people you may know". The only commonality is the IP.
What do you think all the "data scientists" hired by these companies do? IP addresses (or IPGeo) is one strong signal that goes into the "people who you might know" model. One can argue how effective these models are, but it's quite likely that they are found to be useful, for some metrics that the companies care about, like user growth, revenue or whatever. It's also likely that negative sentiment on a forum like HN…
Just because a signal gets you some positive results, does not make it useful. You have to also look at the second-order effects. Does it creep out people? Does it make people less likely to use your service, thereby negating the positive effect of added connections?