As someone else said, Zuck's always been an asshole, long before he had money. In this case, the headline is utter bull, Zuck's doing something else assholish today, but the legal proceeding isn't what the headline claims.
As the article says, there are four half-acre parcels, owned by more than 300 descendants of the people who lived there 150 years ago. That is, each little parcel has about 80 owners, several of unknown whereabouts.
There's no chance anybody is going to track down all 300 descendants and get them to all agree on *anything* - selling or anything else. So the land sits there, of no use to anyone. The legal filing allows Zuck to pay the 300+ descendants for land they probably didn't know they had any ownership interest in, and weren't making any use of.
Why does it matter to him? It doesn't matter much, but consider if you owned a big house, but someone else owned the medicine cabinet in the bathroom, and had the right to come in to the house to get to their medicine cabinet. That of course affects resale value, and it's just weird.