the "hidden community of rats" EY is talking about is this vast iceberg of people who have read rat writing, liked it, have tried to apply it in their own lives (poorly), suffered for it, and then abandoned it (wisely), decrying rationalism in the process (unwisely)
they're real
you don't see them bc they're by definition on the fringes as they don't produce original rat thought or writing, hence are more or less invisible
many of these people find "postrationalism" more palatable bc its structure lends itself much better to being applied by most people