When things are far you can't tell the difference if there are holes or bumps in them. it's either a dot or a big surface if you're close enough. you have to be on he surface of the planet to see the terain
if you really want to know why think about this:
Kernel mode is only worth if it there are loads of data or the data is already there like multiple frames each consisting of millions of pixels, also graphics output/input buffers, DMA. that kind of stuff are all already there.
linux libc is in usermode and it processes dns resolution.I don't know about windows.
We're not talking about performance here. just functionality which I think is fairly good for the matter at hand.
You thought correctly.
Arch users can choose to build packages themselves using AUR that has multiple GUI/CLI frontends like yaourt or pacmanxg. but it's not a mess like debain apt-build and actually integrates well with the standard pacman system.