They exist in fluff, but I personally am not buying the MM for the fluff. I'm buying it to be able to turn to a page or two and find a ready to run monster that isn't a sack of HP and a basic attack. There are plenty of monsters in the MM that aren't like that, why not extend that to some of the basic humanoids that make up proportionally so many encounters?
"I'm not buying the book for fluff. I'm buying the book for things that make monsters interesting."
I guess that's a mindset I can't grasp (note: not implying it's "wrong"). IMO, the
fluff is what makes the monster interesting. I don't need, nor want, each monster to have stat blocks that take up valuable real estate for pretty much the same thing. I already know how the rules work from other areas.
so it seems very odd to me to hear someone say that monsters are boring when they have this detailed:
"kobolds are shifty and crafty, often utilizing clever traps such as clay pots of burning oil or baskets of giant centepedes"
but somehow are not boring if the above is missing, but has this instead:
"claypot of oil: 5' cube, DC 10 Dex save or 1d8 fire damage"
That is, what makes a monster interesting is how it behaves and tactics it might use. Not a stat block that says it uses item X when I could have inferred that (and much more) anyway from the flavor text. Also, if you have stat blocks like the examples Paraxis gave earlier, it implies that's the only thing kobolds can do. Whereas if you give guideance that kobolds behave a certain way instead, it implies they will use anything handy, and not just those specifically called out options. That, and I don't want half the monsters because the page count for each doubles. Not when it's not needed.
Obviously our opinions are vastly different.