Go look at their page for “covenant”, because “real covenant” is a subtype that only specifies the ways it’s different from a non-property covenant https://www.law.cornell.edu/wex/covenant

Quoting from that page:

“The party capable of enforcing the covenant depends on whether the burden or the benefit runs with the land. In other words, only the party who the covenant is designed to help can enforce it.”

Your page spells out the other relevant bits. Real covenants must benefit one party at the expense of another (horizontal privity), so the heirs of the man who donated the land are the benefactors. That it helps (or at least doesn’t harm) the neighbor does not make them the benefactor here because their benefit was incidental (ie they aren’t legally “the benefactor”).

Covenants being centrally registered is a matter of convenience when house shopping, not a declaration that the state will enforce them.

I’d actually bet there are a lot of houses that have racial segregation covenants on them still because the benefactors quit trying to enforce them. I know my city has a bunch of racist laws on the books still because the city quit enforcing them ages ago, city council doesn’t want to spend time revoking laws that haven’t been used in 50 years, and no one has standing to sue to revoke them unless they get arrested for them.