Because Mr. ATO says so. Fines aren't a necessity to produce income, they are issued because you are being naughty.
As Monalisa said, no penalties are deductible, except for interest charged by ATO.
I think there was a case about 10 years ago where a drug dealer had his money seized by (or stolen by) police and he claimed it as a deduction for work related expenses.
Sorry, not relevant, but i thought i would throw it in anyway.