The only reason I can think of is that hand-held mics hide lip-syncing a little better. But is that really true. For newer fans they may be pulled in by bubble-gum pop groups.
Some different examples include - For Mic Drop they used Shure SM58.
Theres plenty of people these days who know all about the voice and the physiology of singing. Now this is actually a good question but it takes a bit of keen eye observation to. We spoke to music producers sociologists and even K-pop idols to explore how the genre. The mics can be seen here in Blackpinks Playing With Fire performance.