However, Ava was not a living human, but a data entity, a virtual life that can exist within any mechanical body. They weren't even sure where Ava was. Could Miracle Force work against such a virtual existence? Moreover, as long as it's data, there's a possibility of a backup. Even if they destroyed the 'main brain' underneath Eden, she could possibly be resurrected at any time from another mechanical body.
Not to mention, even if they instantly killed the main brain, if they didn't annihilate these mechanical bodies, in theory, they would continue to carry out their original command, which is to eliminate the Fools.
So what about wishing to instantly kill all mechanical bodies?
Mu You believed that Miracle Force could instantly wipe out all the mechanical bodies on this planet, but these mechanical bodies had the ability to resurrect, and even if they were killed once, they would be able to come back to life in the blink of an eye.