I’m just guessing here. but really small SMT components are usually reserved for really dense boards. On those dense boards there is no room for silkscreen.
The KiCad Library Team tries real hard to follow existing conventions and common sense.
And how much effort is it to add a few silkscreen lines to your own custom library for 0402 and 0201 and maybe smaller Footprints? Maybe 10 footprints, half an hour work?
But still, this is duplication of effort. Maybe it’s useful enough to have 2 sets of libraries for these components? With and without silkscreen?
On the other hand, removing some silk screen items from items from an existing library is easier and quicker then adding them.
On a side note:
Have you seen some of the video’s from “The Rossman Group”. He’s a guy who lives in New York, makes utube vids about apple products, rants about them, and sometimes also repairs them. He uses “Boardview” software to find components. (Which is based on data from probably reverse-engineerd apple products). And in KiCad you can do sort of the same.
You click on a component on a schematic, and it’s highlighted in Pcbnew. No reason to go hunting for R325 all over a densely populated double sided board.
Some schematic symbols already have datasheet links embedded to somewhere on the 'net, but I prefer to put all datasheets for IC’s I use on my own PC, and (sometimes) also make links to them directly on the schematic symbols.
Quite nice for repair work. You have the schematic & PCB open, and have very quick access to Schematic, Footprint locations on the PCB, test points and datasheets.
You could even argue that software like this makes silkscreen obsolete.