That's essentially what PBR game engines do. They take in base textures/resources (NB: a "texture" doesn't necessarily correspond in any straightforward way to the final image, and shouldn't be thought of as an "image" except in the mathematical sense) and apply all sorts of processes to get a good looking final result.

Not everything can be procedurally generated on the fly (at least with a small algorithm that would run quickly enough on a GPU). At a certain point just providing compressed bitmaps becomes more efficient, especially since GPUs are highly specialised to work with exactly those. Everything is a tradeoff in real time graphics.