How can a voting observer ensure that double voting is actually blocked by this system? Government can whitelist people 10x-voting the right way (real case from Russia).
Issuing 10 passeports to these people is orders of magnitude harder to scale and will have negative consequences (fraud elsewhere) a government is typically less willing to take.
Now an ID card is a valid option so some people have only the ID card and not a proper passport; but there is an expectation that everyone (who isn't e.g. actively hiding from the authorities as an outlaw) would have a valid ID and if they don't it's acceptable to require that they get one before they can fully interact with the rest of the society e.g. government, banking, driving, owning real estate or cars, any legal contracts such as rent or credit, etc.