Referring to the comments that so many people don't pay taxes and tax expenditures that was referred to above.
This is the system we have, and it requires that the tax code do much more then it should which is why so many folks hate it. Therefore, to treat everyone fairly (and somewhat equally) there is one big problem that has to be reconciled. That's child dependents. To reconcile it, the tax system hands back a great deal of tax credits in the form of the child tax credits and the Earned Income Tax Credit. So yes, it looks like many people are not paying taxes, but its because of this reconcilement issue
Then you have the other problem of the standard deduction which is getting rather high. And I believe the Republicans under this bill are again increasing it.