Why did the rebels in Shays's Rebellion make the court their target?
I assume that you are asking about Shays's Rebellion in Massachusetts in 1786. I have edited your question to reflect this. Please let us know if this is not the rebellion you are asking about.
Shays's Rebellion was inspired by the anger of farmers who were going deeply in debt in the years after the Revolution. Their markets had shrunk after the war. Their taxes had risen as the states tried to pay off war debts. The national government had not paid the farmers who were also veterans of the war they way it had promised.
Because of all of this, many farmers were going bankrupt and having their properties foreclosed on. This was done in the courts. The rebels targeted the courts to try to prevent their land from being legally taken away from them because of their debts.