the lagrange point isn't a stable orbit.
That's totally true, but to be fair, it's still more stable and requires less maneuvering than low earth orbit. So if we're comparing the two orbits...
We just need another massive once a millennium volcano eruption. Throw the world into chaos and starve half the population to death while the earth is half covered in atmospheric ash for a year. The slow Thanos snap.
I gotta be honest, that sounds like a less-than-optimal solution. But I like that you're thinking outside the box!