Groupthink

They are swimming in it! The horror is difficult to escape; when one tries to show some signs of human will and independent thought, a mucilaginous tentacle uncoils and yanks the thinker back into the miasma.

Some of them, personality eaten away or submerged (or just merged) into the morass, are happy to be there. They think they are bathing in the eternal spotlight of the sunless mind, with the elder god himself. It is all a mishmash.

It is horrifyingly fascinating.