This is an interesting article, and makes sense to me. What’s clear to me is that people get some kind of a payoff from claims like this, not necessarily financial, but in terms of social status, self-image, etc.
I like to contrast the situation in the United States with Ecuador, where I lived for a few years. There, over two million people still speak Quechua, the language of the Incas. Most of the Quechua speakers identify as “indigenous” people, and dress in an “indigenous” way. However, millions of other people in Ecuador, with almost identical bloodlines, deny their indigenous heritage, because of discrimination against indigenous people.
No payoff = no claim of ancestry.