Souta became a sort of celebrity at Athen's Champion. His feat in subduing the Lernaean Hydra was heard by countless warriors. He's slowly making a name for himself in Athen's Champion and his name would spread out in the future. It's natural that Souta started to attract some attention. His mission record was clear as there was not a single failed mission.
This attention had merits and it could also bring him trouble. If he attracted the attention of those giant organizations then it would be over for him. If it's possible, Souta wanted to go to sub-world and finish some quest before he returned. Unfortunately, Astros Squad's rank wasn't enough to take a mission regarding Athena's sub-world.
Still, he was only quite popular in the warriors' circle. It wasn't enough to attract the attention of those powerful beings. So he still walkout openly.