It's a result of the tradition of insta-kill death trap dungeons like the Tomb of Annihilation. Less common in modern times, but back in older editions players wouldn't even bother making back stories for their characters because official adventures would pile up the bodies too quickly to risk growing attached to them. It really put the "crawl" into dungeon crawl.
Edit: Not to mention the sheer number of monsters disguised as the environment from all directions. When the walls, ceiling, floor, treasure, and air could all be monsters at the same time, players poke everything with an eleven foot pole.