Everyone wealthy

The logic behind shemitta has to be that those who dominate the social structures would consider it wise to allow the body politic, every seven years, to behave as if everyone were wealthy. 

The irony of shemitta is that it fell into disuse because those who dominate the social structures deemed the entire body politic as too impoverished to allow for such behavior under abundance. 

The economy could manage abundance once every seven days but not once every seven years, and certainly not for two years every fifty years.