Some scholars argue that the decline in voter turnout in the 20th century is more apparent than real because in the 19th century

I believe the answer is: voter fraud inflated ballot counts

The voter fraud is initiated by the same persons who go out from their jurisdiction in order to choose a certain candidate more than once. This would make the number of votes for that candidate higher than what it's supposed to be.
By the time we enter 20th century, even though this practice hasn't been completely dissapeared, the security measures that we made drastically reduce the amoun