Its because CS is not cared about as a true science for the most part. Nearly all of the field is focused on consolidating power and money dynamics. No one cares to make a comprehensive history since it might give your competitors an edge.
I have thought that's the common definition and doesn't need much thought...
My dictionary absolutely implies that, it even claims that all the sciences were split of from Philosophy and that a common modern topic of Philosophy is the theory of science. The point of Philosophy is to define truth in all aspects, how is that not science? It's even in the name: "friend of truth". Philosophy is even more fundamental and formal than mathematics. Mathematics asks what sound systems are, what properties they have and how they can be generalized. Philosophy asks, what something truly is, what it means to know, what it means to have a system and whether it's real. The common trope of going even more fundamental/abstract goes: "biology -> chemistry -> physics -> mathematics -> philosophy"
You're confusing computer science with economics. The ahistorical nature of classical and neoclassical economics basically declares that history is irrelevant. Economists do not really concern themselves with economic history, like at all.
