Why do citizen have to register to vote? ?

Voter registration is the requirement in some democracies for citizens & residents to check In with some central registry specifically for purpose of being allowed to vote in elections

This is what i found on google “eightin 1997, the mccaughey septuplets were born in carlisle, iowa. multiple births of as many as eight babies have been born alive, the first set on record to the chukwu family in texas in 1998; one died and seven survived. in 2009, a second set, the suleman octuplets, were born in bellflower, california.” i was surprised about this . i don’t want to have that many babies .