> Because this is not a power granted to the federal government, it is reserved for the states.
If one agrees that this is true, that's not an answer to the question of why not do it; it does affect the mechanics—either a Constitutional Amendment (to do it federally) or a fifty-state compact (do it as a coordinated state-ID system for all state purposes, which is arguably closer to what was described) would be available mechanisms.
“The Constitution doesn't currently allow the federal government to do it” is not an answer to “why not do this in a centrally coordinated way”.
If one agrees that this is true, that's not an answer to the question of why not do it; it does affect the mechanics—either a Constitutional Amendment (to do it federally) or a fifty-state compact (do it as a coordinated state-ID system for all state purposes, which is arguably closer to what was described) would be available mechanisms.
“The Constitution doesn't currently allow the federal government to do it” is not an answer to “why not do this in a centrally coordinated way”.