There's a whole bunch of mechanical and behind-the-scenes dev logic to why the Edlritch are taking over so much so fast, but it's all driven by the story first and foremost :)
The Eldritch have been constantly hinted at being immensely powerful (they have access to Nexus Seeds, words of entry, the Beast seems to be aligned with them, they have deep financial reserves, and so on...) but because they've kept out of local politics and squabbles, everyone underestimated them - including the MC.
So when they tore off their masks and got to work, the Org were completely unprepared. I'd feel sorry for them but, y'know... ;)