Quite simply, because in 1789, "the press" meant the printing press. I pointed to historical references when that began to pivot to mean more broadly "journalism" in general, but in 1789, the printing press was the only meaning "the press" carried at the time.
They of course couldn't have envisioned alternative mediums that the "press" might alternatively refer to. They couldn't have predicted radio, television, and the internet as alternative forms of "publication". There was the spoken word and the written word and that's all there was for thousands of years. The press simply made the written word more scalable.
I understand that Constitutional rights are interpreted by Courts to carry meaning through progressions in technology or society norms. Clearly the spirit of the "freedom of the press" is partly an implied "right to publish" as you say, and as the 9th amendment underscores, the enumeration of certain rights shall not be construed to deny or disparage others retained by the people.
There is no mention of "distributing news and information" with regards to "freedom of the press" in the Constitution. It simply says that Congress shall make no law abridging the freedom of the press. It doesn't justify it or give a reason for it. It's held to be self evident. It should be understood that the U.S. was founded on the principle of "liberty by default". There is no need to justify liberty. The purpose of the bill of rights was to provide extra protections against the egregiousness of government, to preserve liberty, but not to box it in and define it for all time to mean "these specific things."
Clearly the founders couldn't foresee the advent of 3D printing, either. However, milling machines and molds very much did exist. It would be equally unthinkable to the founders to enable the government to restrict the usage of mills and molds on the basis that they might be used to produce arms (another right they saw fit to enumerate), as it would be to restrict 3D printing.
On the basis of the 1st, 2nd, and 9th amendments, and the principles of liberty itself; the 3D printing press should remain as equally free as the 2D printing press.