Because there is no mandated form of ID in the USA (and it was fought against for decades by conservatives claiming it represented unwarranted overreach by the state).
As a result, actually obtaining some form of ID that might be acceptable (the forms vary mostly depending on the political party that writes the rules) can present a significant challenge to some voters, and for some of us, that is an anathema (the right to vote being sacred, certainly compared with the right to drive for example).
Introduced a national ID that the government is OBLIGATED TO PROVIDE for every person, and many of the arguments against it would go away. Currently, no state in the US, nor the federal government, has such a form of ID.
As a result, actually obtaining some form of ID that might be acceptable (the forms vary mostly depending on the political party that writes the rules) can present a significant challenge to some voters, and for some of us, that is an anathema (the right to vote being sacred, certainly compared with the right to drive for example).
Introduced a national ID that the government is OBLIGATED TO PROVIDE for every person, and many of the arguments against it would go away. Currently, no state in the US, nor the federal government, has such a form of ID.