Yet somehow there are so many platforms that will happily subsidise open publication without even taking the initial thousand bucks for letting me in, like Medi

Yet somehow there are so many platforms that will happily subsidise open publication without even taking the initial thousand bucks for letting me in, like Medium, Wordpress, Blogger... Seriously, the only reason why academic publishers can charge anything is their established position, where they are a proxy for gauging researcher's output by administration. Peer reviews are done by volunteers, discovery is provided by Google Scholar and everybody uses PDF anyways (usually printing it out, still orders of magnitude faster than fetching from a library).