Either you have not entered enough itemized deductions to total more than your standard deduction, or,
That usually is an indication that your income is high enough that you are subject to the Alternative Minimum Tax. When you are subject to the AMT, many ordinary deductions such as property tax don't work any more. They reduce your ordinary income tax, but are added back to your AMT income and there is no net change in tax. Once you are subject to the AMT, there is no way around it.
