Why can’t I edit links and directories directly

It is special behavior of bash's cd builtin; the relative file behavior is the natural one. Once you follow a symbolic link, you are in the actual path of the target and the original path information is lost; but if you use bash or zsh to cd there then the shell remembers the original path and uses it in future relative cd commands. But not in relative filename references, because bash doesn't actually know if you intended a filename or something else.

If you look at the cd documentation in bash, you'll see there are -L and -P options which tell it whether to use "logical" (remembering the original path) or "physical" (using the filesystem's idea) paths.

If you need to have the "logical" behavior at all times, you need to use a --bind mount (on Linux; Solaris and other OSes call it "loopback" or other things) instead of a symlink.

A file is an inode with meta data among which a list of pointers to where to find the data.

In order to be able to access a file, you have to link it to a directory (think of directories as phone directories, not folders), that is add one or more entries to one of more directories to associate a name with that file.

All those links, those file names point to the same file. There's not one that is the original and the other ones that are links. They are all access points to the same file (same inode) in the directory tree. When you get the size of the file (lstat system call), you're retrieving information (that metadata referred to above) stored in the inode, it doesn't matter which file name, which link you're using to refer to that file.

By contrast symlinks are another file (another inode) whose content is a path to the target file. Like any other file, those symlinks have to be linked to a directory (must have a name) so you can access them. You can also have several links to a symlinks, or in other words, symlinks can be given several names (in one or more directories).

$ touch a
$ ln a b
$ ln -s a c
$ ln c d
$ ls -li [a-d]
10486707 -rw-r--r-- 2 stephane stephane 0 Aug 27 17:05 a
10486707 -rw-r--r-- 2 stephane stephane 0 Aug 27 17:05 b
10502404 lrwxrwxrwx 2 stephane stephane 1 Aug 27 17:05 c -> a
10502404 lrwxrwxrwx 2 stephane stephane 1 Aug 27 17:05 d -> a

Above the file number 10486707 is a regular file. Two entries in the current directory (one with name a, one with name b) link to it. Because the link count is 2, we know there's no other name of that file in the current directory or any other directory. File number 10502404 is another file, this time of type symlink linked twice to the current directory. Its content (target) is the relative path "a".

Note that if 10502404 was linked to another directory than the current one, it would typically point to a different file depending on how it was accessed.

$ mkdir 1 2
$ echo foo > 1/a
$ echo bar > 2/a
$ ln -s a 1/b
$ ln 1/b 2/b
$ ls -lia 1 2
1:
total 92
10608644 drwxr-xr-x   2 stephane stephane  4096 Aug 27 17:26 ./
10485761 drwxrwxr-x 443 stephane stephane 81920 Aug 27 17:26 ../
10504186 -rw-r--r--   1 stephane stephane     4 Aug 27 17:24 a
10539259 lrwxrwxrwx   2 stephane stephane     1 Aug 27 17:26 b -> a

2:
total 92
10608674 drwxr-xr-x   2 stephane stephane  4096 Aug 27 17:26 ./
10485761 drwxrwxr-x 443 stephane stephane 81920 Aug 27 17:26 ../
10539044 -rw-r--r--   1 stephane stephane     4 Aug 27 17:24 a
10539259 lrwxrwxrwx   2 stephane stephane     1 Aug 27 17:26 b -> a
$ cat 1/b
foo
$ cat 2/b
bar

Files have no names associated with them other than in the directories that link them. The space taken by their names is the entries in those directories, it's accounted for in the file size/disk usage of the directories.

You'll notice that the system call to remove a file is unlink. That is, you don't remove files, you unlink them from the directories they're referenced in. Once unlinked from the last directory that had an entry to a given file, that file is then destroyed (as long as no process has it opened).