I am under the impression that the game gives you harder enemies the more you advance.
At the beginning, I would get mostly red bokoblins, with 1 blue bokoblin per camp, but now, it's mostly blue/black bokoblins, with 1 silver bokoblin per camp. And that is around the 4 main cities, to which you can go at any time of the game, so I guess they should be around the same camp difficulty?
Is it only an impression, or does the game scale up the enemies the farther you progress?