Hi basily,
There is no specific reason no and I wouldn’t read any particular meaning into a manufacturer that isn’t a member of the site.
Membership here is more of an organic process that happens as I get to know some manufacturers better (and of course they get to know me as well) and with newer manufacturers it’s less likely that they would be invited to become members until they have a little longer track record and I come to know them a little better.
There is more about site membership in this article and in post #2 here.
Phoenix