Many programs can fail to change the pty owner back. With devfs, the kernel can chown ptys back to root when a process does not need them anymore. The kernel might be able to let normal users chown their own pty or it might perform the chown automatically. The devfs could appear to contain only those devices that the user has permission for. The devfs could always seems to have just the next available pty instead of all the ptys in use.
Kernel bloating There are always tradeoffs.
When Linus created Linux, he chose the 386 as the minimum hardware. While it would be nice to run standard Linux on the 286, doing so would mean the rest of us must suffer. Those people who can't use devfs because of memory limitations should keep using the unofficial 1.2.14 with a.out and the minix filesystem. They know that designing software for obsolete hardware will make the software obsolete. This scheme won't work with missing dev entries.