I always read that there was a price change for downloads in 2012/2013 in Korea. It became more expensive and because of that the numbers went down for awhile. You could compare it with today’s Melon having less ULs for achieving Top 10 because of some reasons, compared to other years. So this decline between 2012-2014 was widespread for many ig.
that took place prior to 2012 or early 2012 at latest. songs in 2008 could hit 5million downloads like big bangs haruharu. it was already changed by 2012.