This sentence is the final summary of a Throne of Salt blog post about monsters, or more specifically about what makes monsters "monsters".
I could disagree with some of the contents of the post, but instead I'll mention this as a point of agreement. Back when I had delusions of being able to afford college, I took classes in humanities (aka myths/folklore) and anthropology, as well as doing a lot of independent reading in those subjects. One thing you learn very quickly when researching mythology, history of the witch trials, folklore past and present, and beliefs about the supernatural as collected by anthropologists is that magical events and monsters aren't just "weird things that happen", but are always linked to a cause. A transgression, a breaking of societal norms or violation of taboos.
Monsters in mythology are either punishments or side effects of sins against the gods. The minotaur results from Minos breaking his word and not sacrificing a bull to Poseidon. Medusa is transformed not because of her own transgression, but because she is raped by Poseidon in Athena's temple.
In later folklore, ghosts and vampires are the frequently the result of improper burial, but can also be caused by unfulfilled passions (like vengeance) or dying before their time. On the other hand, dying at the wrong time, especially women dying in childbirth or children dying unexpectedly, is often blamed on part-monster, part-witch creatures like the stirge or the penanggalan.
I could go on, but you get the picture. Monsters are basically embodiments of what's wrong in the world, warning signs that something has to be fixed. Where D&D, but also most modern fantasy over the past 75 years, goes wrong is: monsters get stripped from this context and are thus just dangers to fight. This arguably makes sense in fantasy wargaming, such as the fantasy supplement in Chainmail, which offers no explanations for why monsters exist because that's irrelevant in a wargame. It doesn't make much sense for D&D if played as anything more than a skirmish-level wargame.