Why did the Fedora team choose to move /bin -> /usr/bin etc instead of moving stuff out of usr into root (/usr/bin -> /bin)? What is the point of having a usr directory when there is no separation between stuff in usr and stuff in root?

If you want to mount system directories read-only or over a network, it's easier if you put them all in a single mount point. This way you can just mount /usr, instead of having to mount /bin, /lib, and /lib64 this way.

So /usr is now the directory for where all programs installed by the system or package manager gets installed. That actually does make sense.