A different form of scoring (akin to pro boxing) was introduced for this Olympics in boxing. Coupled with the doing away with headgear, the sport of amateur boxing is becoming like pro boxing where the aim is to inflict injury, rather than land clean blows. I don't know why, but this way of scoring seems to make it easier for corrupt judges. A sad state of affairs for the sport of Amateur Boxing.
One factor that also has to be considered is the atmosphere created by the Irish supporters at the Excel Arean in London 2012 must have helped the Irish boxers (and possibly influence the judges). This has been sadly lacking for most events in Rio. Way too many empty seats. Ticket prices must be outrageously high, compared to the average Barzilian wage. A poor Olympics, in my opinion, as a consequence.