You're crazy, it's absolutely the opossite, there hasn't been a generation of girl groups with so many idols with big boobs. In some cases we have several idols rivaling Secret's Hyosung size wise. And in pretty much all cases they're natural, not counting small fake boobs cause they look awful the exception being Jessi who is literally a Bimbo.
I think you notice much more ass, as in proper nice ass like Chaewon, Sohee, etc, due a lot of idols getting so fit due the constant tours these days, not only working out but also following proper diets, even though Korea hates thighs and they lose so much weight in some cases they don't ever recover from that. Miyeon, Winter, Irene, Taeyeon, some examples.
Between 3rd and 4th gen of groups female idols have perfected so much it's beyond ridiculous, my cock can't keep up lmao