Writing libraries is a never ending grind of:
1. trying hard to do one thing and do it well (and failing usually), but ...
2. there are many dependencies that you should allow your user to pass explicitly ...
3. and that’s the problem - you have 0% control on how the library is integrated but receive full responsibility for how well does it work. Even libc could be very different and will not behave the way you’d expect it to.
The big problem of making everything a small well thought-out library is large integration surface + having to be flexible and accommodate for all potential cases of integration.
That’s why we mostly have hundreds of overlapping “fat” libraries - too much trouble and too much integration complexity to split them up.