Okay, I’m going to tell you a thing about Good Omens, but first you have to listen to a thing about physics, but I promise it’s relevant.
In brief and (hopefully) simple terms (and I know it’s WAY more complex than this but we only need the gist of it), there’s this theory that Time is actually a dimension. You’ve got the zero, first, second, and third dimensions that ordinary creatures like humans perceive, and then on top of that we have the fourth dimension which affects us.
The thing about these sorts of dimensions is that a third dimension creature (like a human) lives in the third dimension but is capable of perceiving the dimensions below their own in at least semi-concrete ways. Picture it like this: The zero dimension is a dot on a piece of paper. The first dimension is the same dot, but viewed from the side, where 1D creatures could see it is actually a line. The second dimension is the same line, but viewed from the a second side, where a 2D creature could see it is actually a square. The third dimension is the same square, but viewed from a third side, where a 3D creature like a human could see it’s actually a cube.
Now, say that I am a 3D creature looking at the 2D square on the piece of paper. I am capable of perceiving that second dimension. I am also capable of affecting that dimension; for instance, if I fold the piece of paper in the middle of where the line is drawn. The 2nd dimension can be affected by the 3rd dimension, even if it can’t really perceive the 3rd dimension the way it perceives its own and lower dimensions.
The fourth dimension is reckoned to be Time. Third dimension creatures, like humans, can be affected by time, but we can’t really perceive it the way a 4D creature does. We can’t even really guess how a 4D creature sees the world, because where would you even start? It’s a little bit… ineffable, you might say.
Now, Crowley and Aziraphale, in their true forms, should be at least 4D beings, capable of living in the 4th dimension (time) while being able to experience/perceive the dimensions below their own. Now, I would posit that actually these two exist in more than 4 dimensions, I would say (if we’re following String Theory here) that they could exist in up to 7 dimensions (the 7th being the dimension where one can access multiple dimensions, which explains the existence of heaven/hell), but that’s… complicated.
The point is, the POINT issss…. if they are 4D+ beings, then the third dimension - OUR dimension - is to them what a drawing on a paper is to us. Their corporations are, essentially, a 3D representation of themselves the way we might represent ourselves by drawing pictures on a piece of paper. These projections of themselves would be governed by the rules of the third dimension; including the ability (or maybe necessity) to experience time the way we do while they are here (hence why powerful immortal creatures cannot skip around in time while they have corporations).
Anyway, basically what I’m saying is that god wrote a 3D comic strip and put them in it and is now the frustrated equivalent of a writer whose characters just won’t stop doing things without permission dammit. That or, y’know, she fucked off after creating it and they’ve been writing a slow-burn self-insert fancomic ever since while they wait for her to get back.