I think it is more a question of how lost and for how long. The authors write "modern bladesmiths have been unable to use the methods to reproduce the blades",

I think it is more a question of how lost and for how long. The authors write "modern bladesmiths have been unable to use the methods to reproduce the blades", where the context suggests that "modern" refers to the preceding two centuries. The implication seems to be that, despite the surviving information about the process, it could not be successfully replicated, which strikes me as a reasonable definition of 'lost'. Once the studies described in the article revealed details of the chemical and physical structure of the blades, and, in particular, of the necessity for trace elements to promote the formation of carbides, the authors successfully replicated the process. This leads the authors to suggest that the decline in quality and eventual disappearance of the practice of making such steels was due to the exhaustion of ores yielding iron containing the necessary trace elements. The manufacturers, having no knowledge of the existence, let alone importance, of these elements, were in the dark about how they might rectify the situation. I imagine that all the factors you mention were also relevant, including the relative cheapness of Bessemer-process steel, the relative ease of creating good quality knives from it, and the supplanting of the sword by the gun.