There's a deep principle, I think, that required backwards compatibility eliminates the possibility of needed reform.

One could imagine a "bloat free" OS that eliminates the overhead of the paging MMU and has rationalized APIs and does everything differently.

But you need a userspace and you're going to want to run (say) vi as a text editor and you need a shell so you get zsh to run, and you want "grep" and "awk", etc.

So you have to emulate the old API and in the process of doing that all the old bloat goes back in...