A combination of timing and reductionism. Modern theories of historical critique and analysis that claim to be predictive based on looking at the past generally came into vogue while European colonial empires were a really big deal.

They are tied to a notion of historical progress that takes its example from science, industrialization, and mechanization - that human institutions and behaviors are like machines and have parts and purposes that work to do different things. If you let them work over time they will do these things over time and change the world, and if you change how they work you will change what happens in the future (as opposed to past ideas that were them existing in the context of a natural or supernatural order, being cyclical, consisting of mystical or mystical-adjacent ideas, always getting worse, etc.).

It is not a foregone conclusion in all of historical thought than an empire exits in order to "do" something. You have to get to the point that people are thinking that way in order to arrive at a modern theory that includes what empires "do," and it just so happens that when people got around to that, colonial empires were a really big deal.

And from there you run into a big problem with modern predictive theories, especially about biology and the humanities as opposed to chemistry and physics - which is that there is a lot of noise and chaos and not a lot of signal in observing how these systems work, but that this isn't obvious from somebody writing historical analysis - they often suffer from massive availability and representativeness bias because the sources of information they have to work from are not randomly selected. So it takes a while to arrive at the idea that human systems are pretty chaotic - and even when you do, people don't want to hear it and it's not a very compelling or attractive idea - you get more cred as a thinker for presenting either polemics tearing down something specific or proactive affirmations of some new thing than for ambiguous, skeptical findings.

Anyway - the gist of it is that most people when they build predictive models are very focused on how their model predicts the present from the standpoint of the past. If you were looking at physics, this would be how you would prove that your model reflects reality and that your predictions will come true. You do not have the opportunity to test your theory with future information because the future hasn't happened yet and often takes a long time to get around to happening and you need to do your job. When you're talking about gravity and orbits this is not a problem, because the future resembles the past very closely, and you can even do controlled experiments. In history, this is not the case, and even getting around to tackling the implications of that gap takes a long time.

The present is already bad at predicting the future for humans, we know that. But the past is _also_ bad at predicting the present for humans, it just doesn't feel that way. We get this illusion of confidence in our information because we mostly pay attention to things that seem like they have a point or purpose and have culled out things that seem extraneous or pointless. Because history (or dumb luck that looks like purpose) has done the work of culling out what seems important, we can sift through that to look for the "important" information not realizing what we're sifting through.

Adding to that is the deeper problem that because empires are big and important people assume everything they do has a big and important cause or a sum of sufficiently many different, smaller causes, which is an attractive but flawed way of looking at causality in both history and science.

And sure enough, most models that look to predict the future from the present and validate themselves by predicting the present from the past don't work out. But they sure can be persuasive. This is especially obvious in investing.

So, going back to empires - empires are a really big deal. They are usually among the biggest human things going on at any given time. Because they are big they seem important, and they seem to work like machines, with purposes and parts and ways they can be tweaked or changed or broken.

It would seem not only viable, but critically important, for any modern predictive theory of history to first and foremost explain, from the standpoint of the past, how these empires came to be what they are.

This is such an important part of making the core argument to justify the predictive system, and it seems so unlikely that empires are big beneficiaries of dumb luck and nonsense since they themselves seem on the surface to be so orderly and sensible - that the retroactive explanation for colonial empires can easily become axiomatic for the modern historical critique/analysis models.

1. My predictive theory needs to explain how or why empires came into being in order to be seen as valid about the future, and right now it doesn't.
2. So I go back and look at the evidence available to me about empires, and build out my theory around the evidence so that it's valid and persuasive.
3. What does my theory predict about empires in the future? Well, my theory now explains it!
4. Everybody ignore steps 1 and 2.

But yeah, by a series of coincidences, colonial empires are at the Great Divide in modern historical theory between that which we think we understand about the past and that which we want to be able to predict about the future. So information about them tended to be very selectively framed in any model that saw the light of day, and thus they tend to have extremely different purposes and functions depending on the historical analytical theory you happen to be talking about, very closely linked to the core propositions of the theory, because of the pressure they apply as the "test case" for new theories - more than usual for human institutions and groups, which is already a lot.

And one of the casualties of this is a popular understanding of empires other than modern European colonial empires - the theories are so closely linked to what they say about empires that empires that don't quite fit the theory get arbitrarily in-grouped or out-grouped based on this or that circular axiomatic argument at the heart of the theory.