The editorial boards of papers like WaPo and NYT view their publications as a sort of informational tapestry where every thread is spun to speak seamlessly to a larger narrative. Stories are coordinated like the sewing together sections of a quilt. That story was pulled because it was a snag in the fabric of reality the WaPo wishes to promote. I would bet a very nice steak dinner that someone on Mueller's team made a phone call. For them, the news is a world view to be pushed and Mueller can't have them impugning his witnesses.
Editors quite literally sit together and pick apart seemingly disparate stories to make sure they fit together.
