People choose itemizing when the total of their deductions is bigger than the standard amount.
For a single person with 5,000 charity donations, 7,000 mortgage interest, and 9,000 state and local taxes, itemizing would be higher than the standard deduction.
For a married couple filing jointly with 15,000 in itemized deductions, the standard deduction is higher, so they should take the standard deduction.
In short, itemize only when your itemized total is bigger than the standard deduction.