I'm sure this has been brought up before but I just watched the first 4 episodes and noticed neither group was talked about.
I'm guessing TVXQ was left out cause SM is still salty and is wanting to continue a Chinese like erasure of JYJ from ever existing.
And BigBang because of Burning Sun and illegal drugs connections.
Hell even SNSD only got like 10 seconds of recognition.
According to youtube Super Junior and Wonder Girls are the only 2nd gen groups of significance.