I would say its not actually that difficult, its just constrained by whatever you're trying to accomplish. eg truck simulators dont have you cleaning, because its not part of the mental model of driving. But gas is a very necessary part of it.

Horse cleaning is important for maintenance, but a non-thought in travel. Thus a horse maintenance game would have brushing mechanics and it would be sensible, while it'd be a nuisance in a game emphasizing travel (even slow travel; feeding/housing your horse would be much more appropriate). But the key I think is to realize what the effect you're having on gameplay is pacing, and the mechanic of brushing or feeding or whatever is just an aesthetic/reason around it. So you'd only simulate so far as to render the pace of the game correct, and no more. So you might have feeding or cleaning, but probably not both in a travel game (it'd slow things down too much, and probably be part of the same operation anyways). A maintenance sim would prefer much slower pacing than even a slow travel game would