I can see that, but that sense of the term (which is, I'm confident, the main one in use by a long shot) dates to, like, the aftermath of the JFK assassination and early Roswell-related groups, no? The term itself is older, but I mean the colloquial use of "ideas expressed by kooks and crackpots with excessively-complex and unlikely explanations for things, with an intense resistance to even clear evidence that they're wrong, and far too strong a prior that their unlikely idea is correct". IOW I think you lost that fight by the 70s, at the latest—it's been on people's "radar" since then.
Meanwhile, groups/people/movements that completely match that description are real and it's handy to have a term for that behavior, even if you think it's applied too broadly (and maybe it is). We've got the similarly-abused word "cult", but abuse aside it's still handy to have a way to refer to groups that actually do closely fit the colloquial, pejorative meaning of the term, and there's no way you're going to get people to stop using the word that way.
Meanwhile, groups/people/movements that completely match that description are real and it's handy to have a term for that behavior, even if you think it's applied too broadly (and maybe it is). We've got the similarly-abused word "cult", but abuse aside it's still handy to have a way to refer to groups that actually do closely fit the colloquial, pejorative meaning of the term, and there's no way you're going to get people to stop using the word that way.