why are there so many writers who look down on writing clear, concise prose that would make their work more accessible?
Truth is a busted, rusty tin can
Josh Guilar

Because those writers care more about peer reviews, getting published in academics journals than the general audience. They want to impress other philosophers by using complicated terms and adhering to the academic school standards which are mostly inaccessible to laymen.

Also most accessible philosophers are looked down upon by the academic branch.