They were never intended to be Tai Ji Swords. This type of sword was made long before someone out there misnamed them. This incorrect wording is 20th century terminology
I suppose you could also say it is a western terminology too. I imagine in Chinese they are simply known by a single name rather than Tai Chi broadsword/sabre etc. It probably also comes from the idea of a TC sword pattern, where the term TC morphs into an adjective rather than a noun (sword pattern of TC), therefore giving the impression that there is a specific sword belonging to TC.
However, I do qonder if this is a case of Black sash in pedanticism ;-)