basically since timeline of demon slayer existed before quirks even existed which all the abilities like demon regeneration,blood demon arts,breathing styles,demon slayer marks,bright red nichirin swords,transparent world and finally selfless states they existed but after the war against muzan ended in the taisho period all these abilities are lost through history and time as quirks emerged since then no one in the society of heroes and villains has heard about the demon slayer war in centuries as that history was also lost to time itself
