A single polling station usually only has a few thousand voters. During the day, polling officers at the station processed (signed/stamped/tore/etc) every singl

A single polling station usually only has a few thousand voters. During the day, polling officers at the station processed (signed/stamped/tore/etc) every single ballot that went into the boxes. They also verified every person's ID. When polling closes, why is it enormous human labor to count the votes, but all the processing during the day is not?