This is not a rhetorical question, and it also doesn't have any preconceived answer. It is instead closely related to the question of why there are so few questions on what otherwise seems to be a healthy beta site. Surely there are many relevant questions, as was pointed out elsewhere, so the question is how (or whether) they belong here or whatever.
It seems like most questions on MESE are aimed at the tertiary US audience. Nonetheless, I know few if any US college instructors who even know about this site. Okay, but how many high school, or elementary school, or ... users are there?
So on the one hand it seems to be largely post-secondary aimed (de facto, not de jure) but on the other hand seems to be not attracting that many of that group, and even less of other age ranges. Would it be useful to (intentionally) restrict the audience somewhat, in the hopes of making it seem more targeted and hence more useful? Or does there need to be a bunch of people attending the NCTM meeting to let them know that there is this community who would be very interested in discussions about all levels? (There is the side issue that of course many education questions are somewhat open to opinion, but let's ignore that for now.)
I'm not particularly active here, but knowing how many people storm MSE and how interested the (US) post-secondary community is in discussing stuff, I figure there are plenty of people up for a more focused site; at the same time, I really like the idea of a one-stop-shop for math ed since so many issues really are vertical (raise your hand if you're a college educator who has never seen someone who thinks $\sqrt{1+1}=1+1=2$ is true) and worth discussing across levels as well as among them. But it would be a shame for the site to sort of languish because there are lots of answers but few questions, so I just wonder about whether this is a contributing factor.