A firedrill mentality

The sabbatical year is designed not so much to allow the fields to go fallow as to allow the society to manage the resource depletion. If it were just allowing the land to revive, then it wouldn't be necessary for all farmers to observe the same cycle. The law could just decree that land could be worked only six years in a row, any six years. What the law is actually doing by designating the fallow years as coincidental across the entire society is enabling the building of social institutions designed to deal with resource depletion. 

A nation-wide sheviit socializes the natural environment's issues by turning them into political/economic issues. The same is true for shemittat kesafim. If it weren't about the building of institutions, it wouldn't be necessary for the shemitta to happen all at the same time. 

The institutions the laws of sheviit and shemitta encourage are populist in nature. What they accomplish is a firedrill mentality that enables the general population to deal with resource problems that may confront them without having to come on to the ruling classes. That way, in the event the society undergoes resource depletion, recalcitrance on the part of the ruling classes would not impede the general society's ability to respond in a thoughtful way to the challenges facing them. 

These populist ‘release’ institutions remove the ruling classes from being able to effect a resource curse. 

In the biblical regime, rulers are not absolute. God sends Moshe to Egypt as his messenger to rule not over the Children of Israel but over Pharaoh, and, in a milder way, over Aharon, his brother. When the nation is founded, they have no ruler other than God. When Moshe eventually takes on rulerly responsibilities it is after both the people and God have asked him to, and Moshe's function is largely as mediator, trying to serve as a consensus builder between the two covenantal partners rather than as an isolated actor claiming divine prerogatives or special privileges to his class.