YG is usually the last group to debut their 4th gen groups
with JYP and SM being usually one of the first
but for BG, JYP (SKZ) and YG (treasure) both already debuted their main runner for the 4th gen BG competition
but SM is taking a lot of time, there was rumor about them supposed to debut in 2020-2021
and then i finally understood why SM must take so much time to debut this New BG because of NCTzens
remember how NCT dream was supposed to be a graduation system with member leaving and a new generation debuting
because of NCTzens complaint they had to change all their plans, because the new generations who was suppose to debut after renjun, haechan, jeno, jaemin graduation but then NCT dream change their concept to stop the graduation system
and suddenly SM is left with all these young talented boys that they were ready to debut in their hands with no plans, and considering that
they must have been preparing the BG lineup on the side
they end up with a lineup for their new BG finalize and a lineup who was to be the 2nd gen of Dreamies
which means they might had to change all the BG lineup, to make some of the 2nd gen dreamies debut into this new BG
maybe sungchan and shotaro are even members who were supposed to be part of the new BG but because SM had to change all their plans, and maybe they didn't fit into the new lineup concept and didn't want to get rid of them they made them debut in NCT.
That must explain why after almost 2 years SM still didn't make them debut in a subunit, because it was a last minute decision to debut them
and explain why people were so surprise that they made debut shotaro debut so quickly when he didn't know koreans yet, probably because he didn't fit in the new BG lineup anymore but since he's such a talented dancer, SM didn't want to get rid of him and made him debut in NCT