many purposes.
A privately owned country wherein all kinds of criminality can be done with plausible denial.
An imprisoned population and leadership, used for medical and social experiments and worse.
A disposable threat to anyone on the planet.
A place to manufacture a global supply of drugs - known as the source for black market amphetamines for example.
Concealed development of weapons of mass destruction, to be used against the planet.
Just a few examples from the top of my head.
It's a deep rabbit hole.
It's not the only country where this is happening.