It's just girls being girls. Girls usually gossip about others. And Soyeon didn't really do much, all we know that she said is that "Stitch" should stop wearing Kenzo. Just because Soyeon is in a much more popular group, which had billions of useless controversies/scandals (such as eating ramyun off of a lid), the articles main target is Soyeon. No attention would be on SuA or Euna because they aren't as popular as Soyeon