Because they seem so silly to me.
Where do these courts and prisons get their money? Who funds them? You are stating something that occurs RIGHT NOW IN TODAYS SOCIETY, only through government.
In a free market, courts would have to serve customers who pay them to dispute their cases. Courts that just willy nilly convict obviously innocent people would not only not get very far, they would be subject to legal action by more upstanding courts.
I've written a few posts on private law in an AnCap society, I hope you'll check them out.
*Advancing the Ideas of Liberty Daily*
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