This I think is the heart of the matter; each word or phrase merits a discussion in itself, so I'll save my response for a separate article. But to address the title question: I don't think most people write high concept stories because they like high concept stories. Writers of spec scripts (in my limited experience) tend to think that high concept stories are more marketable than non-high concept stories. Writers of non-high concept scripts often think that they are creating something more original or honest than a high concept storyline. Both directions I think are missteps. "A [script that is centered on a] character we care about [who] confronts complex challenges created by a compelling crisis" (to repeat your essential characterization) and that is well-executed (also your point) should be (with possible exceptions) more marketable than any other kind of script, regardless of the height of its concept. Marketability is more an issue of successfully appealing to a target audience than on conforming to a pre-ordained format of storytelling.