Why is 'do not be unfair' not a precept? And some related questions on precepts
"Do not be unfair" is pretty vague. Do not lie and do not steal, those are easy recognize and not do. What is fair and unfair is subject to debate, well so are perhaps all precepts but I would say unfairness even more so. 

Who says its unfair to sack an employee? The entire system is unfair if it forces a company to sack anybody. The problem isn't with the individual, not in the scenarios you mentioned anyway. Does an economic system accumulate good and bad karma? They're not sentient so they can't follow precepts. 

Just because a home owner feels awful doesn't mean its unfair. Don't get into the game if you don't want to play, meaning don't make loans if you might not be able to pay them. 

I don't know what Buddhism has to say, but escaping the hassle of financial injustice does seem to be one of the perks of becoming a monk. Maybe the Buddha felt great leaving royal life behind and not having to concern himself with taxes, but this is just speculation.