The classic mythological model here is what Mircea Eliade and others called a deus otiosus. In essence, this is a god who has removed himself from the everyday lives and ritual practices of his worshipers.
In terms of religion and myth, the pattern -- well attested in east Africa, the ancient Near East, and sporadically elsewhere -- tends to involve a senior creator-god, an "all-father" like Odin or Zeus, plus a pantheon of lesser divinities with relatively particular areas of interest and influence. The creator creates the world and all in it, sometimes with help of the others, and sometimes simply by creating those lesser divinities as helpers -- or both. Having done this work, the creator essentially lays down the rules for how humanity should relate to each other and to the gods... and then goes back to wherever he actually lives (the sky, the mountaintop, etc.).
From the worshippers' point of view, this means that ritual life is divided into practices that address lesser gods within their spheres of interest. Thus women seeking help with childbirth or pregnancy, or men seeking help with hunting, address their prayers and rites to the goddess of fertility or the god of the hunt, respectively. On certain unusual occasions, principally annual rites of especially awesome dimensions, the senior priesthood (or sometimes an otherwise "secret" priesthood) addresses collective sacrifices to the creator, more or less thanking him for all he has done to make life possible and ordered, for creating the lesser gods, and so forth.
Every now and then, however, really bad things happen, such as a long-extended drought, or a plague, or something like that. The prayers addressed to the lesser gods don't seem to be solving the problem. At this point, the senior priests and the community at large come out to beg for the intercession of the creator.
Think of it like a bureaucracy: you don't go to the CEO when your computer doesn't work, you call IT; when the whole company is collapsing, it's the CEO who is (supposed to be) responsible.
Now the question here simply reverses the perspective on this not-uncommon pattern, asking why the gods behave in this fashion. In addition, it posits that all the gods have receded, not just the creator.
To address this, I would begin with the previously-described deus otiosus pattern, and think about the stories people tell. The question isn't why gods actually do this or that, but rather what people say about such matters. Even in a fantasy world where the gods may manifest directly, they're not especially likely to explain themselves. Why should they?
What I think is lacking from the question is consideration that there may be fundamental disagreement about the gods' actions. If we take the situation you've described, I can see various cults that account for the situation differently:
The gods have abandoned us because we failed to act in a manner they approved. We must return to the old ways, obey every jot and tittle of the old law, and then the gods will come back.
The gods were never really there anyway: they were a fantasy of superstitious rubes. Now we can see clearly that there are no gods, so we should get on with making the world a good place for us.
The gods disappeared for reasons we cannot fathom, because we don't have enough information. We need to keep faith and watch for the signs of their return.
Each of these perspectives will generate mythological material that answers the question posed, but they won't entirely agree -- or even agree at all.