Sad thing is, it was all started because of a fanwar orchestrated in summer 2018 by a few twitter I-Army's with large following who decided to be outraged by YG mentioning BTS in a Blackpink press release, and their outrage was then compounded by DDDD doing very well. Unfortunately it coincided with a massive influx of new international Army's and Blinks who took the twitter fighting as gospel and just accepted that they must hate one if they liked the other!
For Blackpink's first two years Army's were probably the most supportive existing fanbase in K-Pop (Many YG stans were chilly because of 2NE1). It's sad how a few loudmouths on twitter managed to infect countless gullible baby stans with their hate...