Governments exist, and the current standard of identity verification is a laminated piece of paper with a picture on it. If you're giving away free money you might want to have a standard slightly higher than that.
For example, the resource curse implies there will be great reasons for companies to risk gifts of small amounts of money to lots of people in a country about to vote on whether to protect collective assets from corporate theft..
All the weird action committees of US corruption haven't even had the logistics to directly bribe voters of a low population state to piss in the pot. Should they get iris wallet addresses for everyone correlated to scan locations? Is anything the US would do about this beyond the capabilities of Kenya?