That is not the hold back for tax reform, any efforts to simply the tax code gets push back from every special interest that to keep their deductions, and they point to "the others" as "unfair" deductions, so it never changes.

People with kids want to keep the massive deductions for having kids, even though childless people believe that is unfair, people with homes want to keep the deductions for home ownership even though renters believe that is unfair, and so it goes down the line for 1000's and 1000's of loop holes and deductions...

Never a one shall be expunged from the code