Why does our employer include our Per Diem in our wages & why is it taxed. Even after entering my expenses it does nothing for my return.

There were a lot of tax changes for 2018. One of those means that job expenses are no longer deductible on your federal return - TurboTax still asks about them because certain states allow the deduction. This tax change is also why the per diem is included in your wages and taxable.