Henry
Autoexreginated
It's more accurate to say the typically D&D setting has a thin veneer of romanticized Medieval Europe covering a chunky, gooey core of Gelatinous Cubes (self-explanatory), talking giant lynxes (AD&D Monster Manual), ancient machines (see Lum the Mad, Apparatus, Kwalish), laser-shooting floating eyes (Beholder), brain-eating psychic aliens (Mind Flayer), giant insect monsters (numerous), a cornucopia of deadly molds/fungi (more numerous), dinosaurs (even more numerous -- wow Gygax must have really liked dinosaurs!), man-eating treasure chests (mimic), flaming swords, freezing swords, weird magic item stolen from Road Runner cartoons (Portable Hole), and so on.
True, though I hope as a default players can't play beholders or giant lynxes, or buy portable holes.
Besides that, most of that is peripheral to the majority of the game. A character could adventure their whole life and never encounter most of those, compared to a magic sword, or an elemental, or an orc, or a goblin. I'd keep these kinds of things on the fringes, as they were for most of D&D's history.