Probably because Kazushi's the one with most free time

(although from time to time, he also serves as a goggleman for KO Studios).
Baki has his own sets of series (like "Baki Striker", "Baki's", "Baki Real Shot"). So even if he doesn't get to participate in the main series, he gets to fuck whoever he wants later in his own series, lol. And from his Twitter/X account, he seems to have other jobs such as scouting & recruiting new models.
Araki is both a goggleman & a main model of his own. He has his personal platform, does works for other big studios & is also in charge of certain labels, like MOTONARI lately.