Why theremins not in instrument lists on websites?

I was just wondering why the theremin is skipped over in lists of musicall instruments on websites such as: www.basicmusic.net/InstrumentResults.php and www.essentialsofmusic.com/ (This one even has the ondes Martenot, but no theremin.) Is this because the theremin is simply unknown amongst the general populace or is it due to fact that it is not considered a musical instrument(sound effects device)?

While the theremin has made great ground over the past 10 or so years, it's still not thought of as a common instrument. I've been contacting various instrument vendors trying to get them to list theremins in their catalogs, and the usual response (if any) is that they're such a low-volume seller that they can't justify maintaining an inventory.

I think many of us feel a personal challenge to help spread the word about the theremin far and wide. I would suggest that any time you find a site where a theremin listing would be appropriate, please contact them to get it added. I'd love to start hearing some success stories when a site admin actually responds and adds theremins.

As far as I can tell, the above two sites are informative rather then selling/marketing musical instruments. Which, I think that market demand would not make a difference in whether they list the theremin or not. What's so funny is that these sites list some very unusual instruments such as the ondes martenot but no theremin.