Why the parole board, is allowed to extend ones max.
They can extend your sentence beyond the amount the judge gave you? That doesn't sound right, but I'm no expert. I assume you just mean their denying you parole? (IE you got 10 years, and 7 years in they say nope, you got to stay.)
if one is deemed unsuitable for society this is what their doing now and or sending them to a mental hospital you must be referring to a molester/rapist or a violent person ?
If the board decides that you are a danger to society, then it can extend your time. Depending on the state, the board might even send you to a psychiatric or mental hospital.