Thats because it was invented to make the models work. By definition it cannot be observed directly so it's never been observed directly but this presence of immense amounts of invisible, intangible stuff is needed to make the models fit actual observed phenomena. It might even be real. But currently it's a hypothesis that explains some otherwise catastrophic model issues for celestial mechanics.
But this experiment didn't detect dark matter, it just caught a freak event that that had nothing to do with dark matter and just happened to occur in an apparatus they were monitoring hoping to find dark matter so they saw it.
Trying to avoid all the implications that would occur if celestial mechanics (Newton!)is wrong!
My bet is before that happens they’ll detect something that sort of fits the current theory or a serious addendum to celestial mechanics theory will be found.