IANAL, but my understanding is that it's extremely difficult to successfully sue someone for libel in the US, mainly due to all the First Amendment issues that come with letting the courts adjudicate what can and can't be said.

Professionally-trained journalists are very aware of libel concerns and are taught to stay within the law. The NYT's journalistic standards may have taken a nosedive in recent years but I'm sure they can still afford good enough lawyers to avoid getting sued over a hit piece, even one as sloppy as this.