@stib @benroyce @nuintari @Strandjunker I will add that the situation is similar in Thailand. They have mandatory voting also, a similar turn out and everything.
Thailand did have a major problem with bribery in voting (yes, there were/are arseholes rich enough to bribe the majority of an electorate). Always was illegal, but ways were found. I'd wonder if the case isn't the same in the USA these days. This seems to have mostly been fixed in Thailand after a secession of military coups, an unfortunate path to where they are today.