They are not doing it because they came out with the idea to help their little town band, they were told to do it by the giant corporations behind those bands, BTS and BLACKPINK being perhaps the two most insidious in this regard, it's literally an unpaid job and those companies aim for the teenage girls and boys who who are the most unhealthily obsessed with one or more members of the band to do it, by telling these thousands of impressionable teens that the way to show that love is to become the equivalent of human spam bots.
