|Just another Monster Manual, really|
The world (including all associated planes) is a created artifact, made and maintained for the pleasure and entertainment of entities who, to the created inhabitants of that universe, are, to all intents and purposes, gods.
The situation is very similar to that shown in the recent series, Westworld, though on a larger scale. Very similar indeed. Or perhaps it would be closer to the "Hells" in Iain M. Banks' Surface Detail.
Some of these entities, who for the sake of convenience I will just refer to as gods, get their jollies by physically interacting with the created universe and its inhabitants. Some restrict their interference to working from outside, operate via proxy creations, and manipulate the conditions of the world to create circumstances beneficial to their agendas.
The key thing to note about both of these groups is that they are playing a game. They are playing for points. Some play very seriously, some just dabble for a bit of fun. They get more points for actions where they are physically present, because when they are physically present, they are in physical danger. Still other of the "gods" are simply observers, watching purely for entertainment but having no stake in the game, nor any way of influencing events in it.
But regardless of the stakes of the game, it's still a game, and the created beings who scurry around the world are just playing pieces.
So basically, all the actions, purposes, plans, schemes, loves, hates and so forth of all the created inhabitants of the world are futile and meaningless, existing only to win or lose some entity a few game points or to provide an evening's passive entertainment. Bummer.
The thing is, that's irrelevant to them. Even if they know the true state of affairs (and some of the more potent characters in the farce have at least an inkling that it might be so) they still have to live their lives. They may be playthings of the gods, but that doesn't mean they don't have to eat and shit and make a living.
So, there it is.