Devil's advocate: I think the point is not to solve a problem the users have, but rather a problem the company dabbling in crypto has, e.g. that no user benefits twice from one-time offers, this kind of things.

You don't offer up the biometric data itself, you offer up something anonymized and derived from it (think a hash of your biometric data).

"Worldcoin says it eventually wants to erase the iris images to protect the privacy of those who sign up for its currency. If perfected, the company says the technology will distill the image of each set of irises into a unique string of letters and numbers, called an iris-hash, to be stored in Worldcoin’s database. As the company’s data consent form states, data gathered by the Orb will be used for “purposes such as training of our neural network for the recognition of human irises.”"

Because in our current environment, a data breach of your government issued ID can have more negative real world consequences through various forms of identity theft than a data breach of your retina can.