The Titans in the MonsterVerse (including and especially Godzilla) have always been portrayed as the living embodiments of forces of nature on Earth.

Godzilla is the one that maintains the balance as the alpha, but every Titan plays their role. So, if humanity, not another Titan, ended up being the ‘ultimate villain’ of the Godzilla X Kong MonsterVerse trilogy, that would allow the series to send a powerful metaphoric message to audiences, as they’d witness humans wearing destructive machines of their own making literally fighting elements of Mother Earth incarnate.

Though beyond the metaphorical significance of this potential trajectory for the Godzilla X Kong franchise, it just makes sense that humanity would want a hand in its own potential extinction every time Godzilla or Kong needs to be called to action.

No human weapon works against Godzilla or the other kaiju, leaving humanity vulnerable to attack at all times (which is essentially the cornerstone of this entire franchise).

Now, however, there’s a mech-suit design that’s proven to be effective against Titans, and there’s just no way the governments of the world will let that go to waste.