In Jain understanding, Mahavir Swami did not intervene violently or physically to stop the killing because Ahimsa is absolute. A Tirthankar does not save beings by causing harm, force, or attachment-driven action. His path is to teach, awaken, and show the way to liberation, not to create worldly rescue by violence.

Regarding the Jain munis who were killed by Gosala or by hostile forces:

• A monk’s body is temporary, but the soul’s karma is what matters most.
• A true Jain muni accepts suffering with equanimity, without hatred or retaliation.
• Mahavir Swami, as an omniscient Tirthankar, is understood to have seen the karmic unfolding, and did not interfere because breaking the law of karma is not the Jain path.
• If he had tried to “save” them by force, it would have involved himsa and attachment, which contradicts the conduct of a Tirthankar.

In Jain Dharma, compassion is shown through:

• preaching dharma,
• removing ignorance,
• helping beings avoid future bondage,

not by using violence to stop every worldly event.

So the deeper reason is:

Mahavir Swami came to liberate souls through right faith, right knowledge, and right conduct — not to alter karmic events by force.

If you want, I can also explain the Jain view of why even an omniscient Tirthankar does not “interfere” in karma in a very simple way.