The reason is simple: Because that's an argument for a courtroom, not the court of public opinion.
Nowhere in the Times story is there an allegation that Trump broke the law. What he did — reporting $916 million in losses in 1995 and, therefore, opening the possibility that he didn't pay taxes for the following 18(!) years — was legal. No one questions that. Here's the key paragraphs from the Times piece on that front:
The 1995 tax records, never before disclosed, reveal the extraordinary tax benefits that Mr. Trump, the Republican presidential nominee, derived from the financial wreckage he left behind in the early 1990s through mismanagement of three Atlantic City casinos, his ill-fated foray into the airline business and his ill-timed purchase of the Plaza Hotel in Manhattan.Tax experts hired by The Times to analyze Mr. Trump’s 1995 records said that tax rules especially advantageous to wealthy filers would have allowed Mr. Trump to use his $916 million loss to cancel out an equivalent amount of taxable income over an 18-year period.
Not illegal. But man oh man, does it look bad in the context of a presidential campaign in which Trump is trying to argue that he is the voice of the everyman.
What Trump did is take advantage of loopholes in the tax laws available to the very wealthy. Period. He had lost oodles of money through a series of failed business ventures but was able to wriggle out of that problem by (a) declaring bankruptcy (he declared bankruptcy four times in 1991 and 1992) and (b) using the tax code to his advantage.
That doesn't sit well with the average voter. Remember that at the core of lots and lots of people's frustration with Hillary Clinton and the political structure more broadly is the feeling that the elites in this country are operating under an entirely different set of rules that benefits them but not the average person.
That's literally what Trump was doing with his taxes. The spin that he was a "genius" for finding holes in the tax law doesn't change the fact that Trump gamed the system for his own benefit. Ditto this argument from Trump's campaign: "Mr. Trump knows the tax code far better than anyone who has ever run for President and he is the only one that knows how to fix it." Sure. But that doesn't change the fact that Trump used his wealth and his
lawyers' knowledge of tax laws to create a very advantageous situation for himself, despite the massive losses he had suffered.
Hillary Clinton's campaign is smart, and so they quickly released this ad Monday designed to keep attention on Trump's tax problems.
What's fascinating to me is that this confusion of legalistic and political answers by the Trump campaign is the very same thing that Hillary Clinton has done for the past 18 months on her private email server. Clinton was forever insisting that she had broken no laws and that she was well within the law to do what she did. That, of course, was never the point. The point was that for a candidate already struggling with questions of honesty and transparency, setting up a private email server and then writing it off to mere "convenience" badly hurt her in the court of public opinion.
Same goes for Trump. His current legal argument on his taxes badly undermines the political argument — elites are gaming the system to help themselves and hurt you — he has been prosecuting the entire campaign.
It's possible that this is the nihilist campaign — that nothing matters. But if major revelations — and how the candidates react to them — still have the potential to change minds, then Donald Trump has a massive problem on his hands with this tax story.