Maybe it's because one event as tragic as it was only happened to one person in one city where as thousands of people were killed on 9-11 and thousands more friends and family members effected by it, not to mention those rescue workers hurt by the residual effects of breathing in asbestos and toxic air which gave them cancer. It's a lot easier for people to grasp the government murdering one man who choose to seek the highest office in the land where he'd naturally have a target on his head then to murder thousands of innocent people. That's a level of evil that's too difficult for most to wrap there heads around.
This plus plausibility.
Some of the lesser parts of the JFK conspiracy are much easier to swallow. "second shooter", "Castro/Communists", "mafia", "grassy knoll" and the explanations for each are all plausible. And even some of the bigger picture conspiracies only involve a handful of people.
9-11 on the other hand doesn't have much that's even plausible plus it would involve thousands of people being in on it and that's just silly.
FTR, I don't believe in conspiracies around either (or any conspiracies really)
Agreed. I don't believe either but the JFK theories are infinitely more plausible.