Display Moreyou have to have what others don't. if no one else is good at physical sales and you're 3-4x ahead, all you need it to be relatively comparable for everything else (not getting into all the variety show, cfs, etc dominance).
the only thing girl groups had were better digital sales from 2011-2015 but none of them were able to maintain for very long.
t-ara's hot digital streak was 2011-2012 (agency was too messy tho)
kara exploded in japan for 2-3 years
sistar had summer hits but were seasonal
2ne1 was the closest competition but YG didn't consistently promote them
some people could argue that there was no national gg from around 2013-2015 but snsd was always the top girl group, so in the absence of any serious competitors they extended their reign
Didnt Kara has pretty good sales in Japan, I read their stats, they were the best selling gg before Twice in Japan