Well... people will always make fun of things for being popular. (especially if it is popular between girls)
This is kind of like when Justin Bieber and One Direction got hate.
I remember 10 years ago, when I got teased by my classmates for liking it. (back then when kpop was less popular)
It's because BTS are more popular now in India in comparison to 2018-'19
Yes, I’ve seen this a lot for many groups and individual idols—the more popular they get, the more hate that gets thrown around. It’s really disheartening.