There is so much driver and feature spam in the Linux codebase. I really wish a beautiful, minimal microkernel approach would have won out.
Why can't distros be a package of microkernel + drivers?
Why can't distros be a package of microkernel + drivers?
The first week or so of the process was learning how to go from a new Debian machine (with the expectation we'd only used Windows or Macs before) through "git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git" (not on Github at the time) to finding the function called by "man 2 fork" and navigating the source tree/unmasking preprocessor stuff to show the actual implementation. Yes, you can easily make a wrong turn if you're trying to do that on your own. But the actual linux/kernel directory, which has most of the parts you'd want, isn't that much larger, and a lot of the difference is modern requirements like power saving and security.
Performance. Basically, the required amount of context switches (since all drivers run in user mode) impacts performance and cache use in a negative way compared to monolithic kernels. Whether this is still a significant issue with modern designs, I don't know, but that was the argument back in day (i.e. the early 90s when Linux came about).
They are built (usually) at the same time as the kernel, yes, due to the lack of ABI stability guarantees, but most drivers you don't use won't take up any RAM.