Because they thought their competition might beat them to it:
"Salter blamed the New York Times' obsession with this sort of intramural scorekeeping as the paper's real motivation for going ahead with a story "they'd already spiked." "They did this because the The New Republic was going to run a story that looked back at the infighting there," Salter said, "the Judy Miller-type power struggles -- they decided that they would rather smear McCain than suffer a story that made the New York Times newsroom look bad.""
In my previous post I mentioned that we really shouldn't care whether or not McCain was having an affair with a lobbyist, and that the other info in the article was more important. Let me also back that by saying that just about all of these assertions by the Times regarding said alleged affair is speculation. As MY says:
"...the Times's effort to substitute innuendo for making a straightforward true or false assertion is seems like a pretty shameful attempt to set up a Kaus-like presumption of guilt. If they have reporting they're willing to stand behind of a McCain-Iseman affair, they should publish it. And if, as seems to be the case, they don't have the reporting, then they shouldn't write the story."