You could export the Linux filesystem, but the foreign system might not support backing up devices. That is wrong of course, but it is not a dumb mistake either. We should not torture newbies. Directory lookups on the ext2 filesystem are linear, so it is very bad to have so many entries. These huge linear directory lookups slow down Linux.
Every update means a disk head seek, which reduces Linux disk performance.
With the devfs, the root filesystem can be read-only. With a devfs, Linux device names become better standardized. Device files and symbolic link storage is awkward and very slow. The devfs would eliminate the overhead and reduce the umsdos requirements. When a pty is needed, root must change the owner.