Even though devoid of knowledge concerning the Borrowed Might potions' intricacies, the Sages understood their limitations.
They initially chose to safeguard the Rankers before refocusing their efforts on a foe they believed they could overcome collectively.
This was the governing factor behind their decision-making process. Eren had subtly given them false hope by drinking the Borrowed Might Potions in front of them before extinguishing their lives.
The Sages from both sides had been locked in battle before Eren's intervention. Even without leaving their positions, they were already grappling with fatigue and significant mana expenditure.
This was the reason why Eren wanted to halt executing the Lazarus Project unless and until the Sage-ranked entities from both sides got involved with each other.