So my personal thoughts on what I've read about the Blob and factions:
The Blob is basically a large living organism, and The Earth is a tiny speck that has been absorbed by it. Not like food that person has eaten, but rather like the part of food that gets broken down and absorbed into the body.
The Zombies are basically like the immune system and digestive system. They break down the living organisms, which are generally human survivors.
What this means is that, probably unknown in the first couple years, is that human settlements can only grow to a certain size before they actually attract the Zombies, in the same way that a small amount of bacteria co-exists in organisms, yet a large amount triggers an immune response. Or that a small crumb of food goes unnoticed, but a larger amount of food draws attention.
This sort of conflicts with the thoughts in the design document about the Old Guard, who are supposed to re-establish themselves, although it should become obvious to survivors of several years that larger groups get attacked. I imagine many survivors in year 5 probably have adopted a theory/belief/rule that no group of survivors should exceed x population in order to survive. Any faction still around has probably adapted to that reality.
...then again, maybe the Blob is so big that it doesn't even notice on an involuntary level a human civilization has taken over the whole New England area. Just like most people don't acknowledge dead skin cells.