I'm %100 sure he knows the other ways, but I (again) assume his limitations are technical. To start the TK17 takes around 5 minutes with a mid-range computer, now imagine working with such thing to do animations. Its freezing - not responding for couple mins and sometimes it errors creating scenes. Its both cpu and gpu heavy, because of the modifications.
He could rather record the actual animation as a video, using the tk17 itself would make it worse but capturing it with apps like OBS would also fixe frame rate issues and would make animation quality much more better as he can edit the video afterwards.
But with this option would make things take longer as he would have to import each and every 3D object into tk17, like the bed the characters gonna have sex on. Now it would take 10 mins to start the tk17 app itself with lets say mid-range computer.
Game development is just decieving the player, currently Chyos is decieving us to believe that we are watching 3D objects animate, but in reality, the characters and all the other objects are just 2D pics
The other options would be giving up tk17 which would mean changing the style of the game completely. Going for Daz3d or Blender or even (i would not recommend) Honey Select would make things 100 times easier, but he's quite deep into the game now and it does not seem to be possible. (I would do it even though knowing I would face a backlash from the fans and players)