While overlooking a Silt Strider, it came to my attention that I don't think I've ever encountered a wild one, and everyone I've spoken to has pointed out that only the more civilized cities seem to have access to them, and certainly not the Ashlanders, who would enjoy a boon from having such a large source of manual labor.
Therefore it was proposed is it possible that "silt strider" is simply the term for a domesticated form of netch that has been bred down with the purpose of acting as a form of cargo transport? And therefore we don't see them in the wild, because they require a special degree of Dunmer breeding?