Eren needed to be a lot more careful in Labh Salem.
He especially had a lot of restrictions in using his demonic powers now that he had decided to join the divine faction.
Keeping the Demon Princes in check was more important for the current Eren than removing them from their respective positions. He could impose them with restrictions if things really came down to confrontation, using the laws of the demonic pantheon.
The Demon Princes were more dangerous to Eren if he were to free them from their current positions and responsibilities. Plus, he was not able to handle any responsibility and carry the load on his shoulders if he were to vacate a seat. He was nothing more than a Demi-god.
