Possible explanations:
I think in BTS case they were seen as just another kpop boy group. They are huge yes but they are more TVXQ while BigBang is more Epik High. Meaning BTS is an idol group and more fandom driven by female fans while BigBang is seen as artists who appeal to the general public because of more artistic music.
Blackpink case is easier to solve. Girl crush doesn't sell in Korea as well as cute concept. This is why 2NE1 lost to SNSD every single time.
Plus these two groups have been out a lot longer so naturally more people know them and have grown to love them.
BigBang and SNSD are still to this day the King and Queen of Korea.