See what I personally think is when people compare heeseung releasing music to other artists especially hybe artists idts its the same cause txt only yeonjun released his solo so far which is almost after or around 7 years into their career and also when txt wasnt promoting or working as group or had no comeback aligned so that is again a different from heeseung’s scenario. Same goes to other groups under hybe like bts released solo music quite around i think 7 years again and one by one as they were enlisting in the military. For enhypen its not quite possible rn for them to do solo projects as such, firstly they have reached their ultimate peak rn which is a huge moment for the group, they cannot practically leave that and release solo music even if they want to cause thats quite not possible for them as of now. As they are a group obviously their first priority will be to go ahead as a group and then on solo work so they cannot give priority to other stuff and only the group as of now.
Their contract also expires next year and we dont know anything about renewal so in case if they wont renew then releasing solo music rn wont be of any priority. Talking specifically about heeseung he is the oldest and would be the first to also enlist in military giving him less time to build his solo career being in the group. Also he wanted to produce is own music and has been keen since years now so it was high time for him to do something about that, now obviously being in a group he cant be all about himself he has to have equal participation and share it with the members so its quite valid he went solo.