That's why, despite what many people want to believe for some stupid reason, he didn't infiltrate alone!
Either way it's not just collateral damage from a Shifter Battle right smack in the middle of the Marley Capital/Liberio. It's about what that battle means:
We may have learned some shocking revelations about who actually rules Marley but Zeke doesn't know that. What Zeke knows is that all Eldians under Marley control are constantly under the threat of being labeled "Useless" or "Not worth the Risk."
Let's say an unsanctioned TItan Shift occurs in Liberio, and then following that several more, and then a massive Titan battle that wrecks everything. From Zeke's point of view how do you think the Marley government will feel about this? Do you think that having these FILTHY DEVILS around is worth it anymore? Look what just happened.
Collateral Damage is nothing to complete extermination.