The US constitution is but one of many sort-of democratic frameworks. And not overly democratic in its consequences (see gerrymandering, and the effects of the electoral college, or just all the problems with first-past-the-post even in theory).
So while HOAs have their obvious deficiencies, your attack is one of the weakest complaints imaginable.
Does every member of a family get a vote? How about every adult? Or is it just one vote per household?