Why did the Congress of Vienna redraw the boundaries of some European countries?

To encircle France with strong countries.

The main goal of the congress of Vienna was to keep a lasting peace in Europe. To do this, they created the principle of legitimacy which restored all monarchs to the throne who were in power before Napoleon, which is a very conservative law. Some boundaries were drawn for the same reason, and others to keep European balance of power, which means that one country should not be stronger than another.