Why don't Planar Bound Outsiders Cheat?

[blackwindbears]

Keep in mind that killing a fiend isn't actually that much of a threat to them, and doing so would actually just make you an enemy that will be free to hunt you down as soon as they reform on their home plane, you would instead be safer keeping them permanently caged up, but even that becomes precarious, since the binding circle only lasts 1 day/level, unless you find some way to make it permanent, like some wondrous architecture binding circles or something like that. But even then, it's a delicate cage that could be broken easily by some mishap like an earthquake.

Two questions:
1) What, in your view, compels their obedience to the letter of the agreement after let out of the circle?

2) Called creatures either *die for reals* (Core) or in the case of devils take 99 years to reform (FC2), on the case of demons reform but likely demoted (FC1), how would they be free to hunt you down?

Edit: Further, looking at the demons, almost none of them have plane shift. It seems to me that the ability to exact their plan of vengeance depends a lot on top level cosmology questions, like, how well known are portals to a given material plane, how accessible are they? If trivially accessed then it begs the question, why isn't the material plane overrun by demons?

In all other respects I think your explanation broadly makes sense. The "unreasonable commands" clause seems to be a problem for a hard #2 (most powerful, unbreakable enchantment (compulsion) effect). If a wish won't end it, what could possibly constitute unreasonable?