My best guess is a combination of things. A non-polemic speech style, a pernicious habit of forgetting not to use multisyllabic words, and above all a take on the universe that is decidedly orthogonal to a good chunk of the population.
The pessimistic alternative is that what I've said is too dull to inspire comment, slipping immediately from memory before my audience can even form a reply.
Removing the staple from my hand-and-forehead, it's part of why I find 'small talk' so unpleasant. Not only is my natural inclination not say much, but when I do say something and people just look at me, it's even more disconcerting.
In person this doesn't happen much, with closer friends at least. I imagine most people who know me very well are aware that I've never met an 'uncomfortable' silence. Silence is quite cozy, good for thinking or just being companionable with someone. My friends all share some aspect of my orthogonality as well, which helps with that part.
In print/online it's harder to tell, and it's there I'm more likely to suspect boredom on the part of the beholder, since there aren't any handy body language cues to tell me otherwise.
In casual social contexts I sometimes feel like I've lost all power of communication, though. I do okay in a work context, unless it's a non-working work context, like someone's retirement send-off.
It certainly helps make flirting nigh impossible.
It's supremely frustrating to someone with as much hubris about language skills as I have.