Twenty-odd people were killed in Boston's North End. We have discussed before, under the story of the Edmund Fitzgerald, why some tragedies enter the popular imagination while others are quickly forgotten. I think in this case, the specificity of the molasses is key. The news likely was reported at least a bit in other parts of the country, and in New England it would have been big news all week.
The interpretation now is that it was forgotten because it was a poor immigrant neighborhood and Who Cares About Them? It is believed that we buried news about greedy capitalist bastards and their victims back in the day. Yet I doubt that is the case. It would likely have had a comic side even then, which might have given the story legs, but at root, people in Birmingham or Davenport or San Diego would have thought we don't have any molasses tanks here, and none of my relatives lives near a molasses tank. Nothing to worry about.