I'm guessing this particular item got caught up in a general "sweep" of things being sold with the various predecessor names and logos on them. I'm no intellectual property lawyer and the law is probably complex and not necessarily rational, but as I understand it if the holder of a copyright or trademark doesn't enforce their rights they risk loosing them. So some low level clerk deep within the BNSF law department was probably tasked with sending out form letters to every vendor selling something with one of their railroad names or logos on it, with little attention to the context or details. In this particular case I would guess the copyright law doesn't apply (if challenged) because what is shown is a historic photograph and the text is simply historical info, it is not a logo or some other representation that suggests NP sponsorship. I would think (but perhaps am wrong) that it is little different from putting the picture and info in a book that will be sold. Zazzle complied because it's not their fight. Of course, the problem with this type of heavy handed intrusion on others' rights is you can get away with it unless the other party chooses to challenge it in either the court of public opinion or a court of law. All of which is probably not worth it. But hopefully with a little ingenuity there are ways to ignore it and work around it. Sorry for the long winded diatribe, but this kind of corporate nonsense is fascinating.
JBWX