It is both amazing and deeply concerning that one corporation has influence over 1/4 of the world's population. It is even more concerning when you consider the outsized voting power of 1 person at that company.
Facebook is a platform. They don't do a lot of attempting to influence, as far as I can tell. Consider Google as well, which probably reaches even more of the world's population. Or Microsoft. Apple might be getting close, too. Or plenty of non-tech companies, as the sibling commenter points out. Coke, Samsung, Frito-Lay, etc.
When a single platform has the eyes and attention of a third of the world's population each day, even the smallest things, purposeful or not, could cause a ripple of change.
I would argue Coke, Samsung, Frito-Lay, etc are different. They can't make instant changes or do AB testing on a scale that Facebook can. Facebook could give a single page over to an algorithm that runs millions of experiments a day to learn how best to influence a person in a certain way, iterate on that and continue. A single engineer, with their scale and data, could set this up given the proper permissions.