Because they're all pieces of one whole, scattered throughout all of these different places in space and time and stranded wherever they ended up.

Their power comes from chaos, which they seek to gather in order to sustain themselves. They do that through their agreements, and the way they can cause ripples that turn into waves by being somewhere they don't belong and affecting that world around them.

Even our agreements feed them that chaos, because our form of it is being here, being sent to those places where they are rather than where we're supposed to be, too.