No matter how strong you get, guards are always on par with you. Aka Level scaled

While your out fighting dragons they are probably training and getting stronger.

I just find it weird that every monster in the game is somewhat easy after a certain point, but town guards seem to keep growing stronger.

Don't want it to be like morrowind, now do we?
after a certain point, you could commit any crime you wanted with impunity, since you could massacre the whole guard force with relative ease