My guess as to why EKI doesn't offer various handle materials in the production market is as follows.
From a production and sales standpoint, they offer quite a few knives already. They have their base models, many of which are offered in both spearpointA) and Tanto(B) versions. Then they offer two different blade coatings, satin and black, which can be either serrated or non serrated; and finally the knife can have either black or green handles.
Each of these variations essentially doubles the number of knives they offer.
To add one more variation, such as handle material, would double the number of possibilities again.
The resultant sales are not likely to increase a whole lot. Few people (mostly those who frequent this forum) would want to buy an additional knife, just so they could have the micarta handle,or whatever it may be. Along the same note, a different handle material would not convince Joe Knife-user to spend that kind of money on a quality knife, if they aren't willing to buy one with the G-10 handles originally.
Anyways, that is my two cents. Anyone want to rebuttle?