That's because the JFK conspiracy theorists didn't call themselves "truthers" like the 9/11 conspiracy theorists.
Teabaggers named themselves before Democrats began using it derisively. The double entendre was an obvious connection and why wisdom should be employed when naming a movement.
https://en.wikipedia.org/wiki/9/11_truth_movement#Name
Name
Truth movement sticker
"9/11 Truth movement" is a term that has been applied to loosely affiliated organizations and individuals that question whether the United States government, agencies of the United States or individuals within such agencies were either responsible for or purposefully complicit in the September 11 attacks. The term is also being used by the adherents of the movement, who call themselves "9/11 skeptics", "truth activists", or "9/11 Truthers", while generally rejecting the term "conspiracy theorists".
https://en.wikipedia.org/wiki/Tea_Party_movement
"Teabagger"
Some members of the movement adopted the term as a verb, and a few others referred to themselves as "teabaggers." News media and progressive commentators outside the movement began to use the term mockingly and derisively, alluding to the sexual connotation of the term when referring to Tea Party protesters. The first pejorative use of the term was in 2007 by Indiana Democratic Party Communications Director Jennifer Wagner.
The use of the double entendre evolved from Tea Party protest sites encouraging readers to "Tea bag the fools in DC" to the political left adopting the term for derogatory jokes.[253][255][256] It has been used by several media outlets to humorously refer to Tea Party-affiliated protestors.[257] Some conservatives have advocated that the non-vulgar meaning of the word be reclaimed.[253] Grant Barrett, co-host of the A Way with Words radio program, has listed teabagger as a 2009 buzzword meaning, "a derogatory name for attendees of Tea Parties, probably coined in allusion to a sexual practice".
