They first went along with the hoax. They should never have done this, as the Rubin Erdely article was obviously a hoax. But damsel-in-distress articles just sell very well (see mattress girl, also obviously a hoax), and few people have the stomach these days to confront the twitter/tumblerina/feminist hate-mob. An independent journalist (whose name escapes me at the moment) was the first to have the guts to point out the obvious. The Wapo and NYT then, very gingerly, and clearly reluctantly expressed some doubt. As far as I'm aware they also never did their journalistic homework and do investigation of the UVA hoax of their own ... too expensive I guess ... why think for yourself when you can simply print somebody's PR material?
