Many deductions have to be supported by forms that are already provided by third parties both to the taxpayer and to the IRS. There&#x27;s no reason these couldn&#x27;t be included in pre-computed taxes sent out to taxpayers.<p>Its not done in the US because the makers of tax prep software and providers of tax prep services have lobbied against it the several times it has been proposed, and with a very substantial industry that is completely threatened, they have plenty of motivation to lobby hard.