Why doesn't `su -` re-read /etc/environment?

Question

I have the following line in /etc/environment:

AAABBB=cccddd

When I login using the text console, the variable is set, I don't even need to reboot. But if I do su -, the variable is cleared. Why is that?

I have this on ArchLinux and on CentOS 6 and 7.

here grawity says:

Logging out and back in would apply the changes

But issuing the su command with dash is that very thing!

I'm really unhappy that su - clears the variable. Is there a way to make su behave better? One workaround is to duplicate the record in /etc/profile.d. It's not enough to have the record in profile and not /etc/environment, because there are cases when profile scripts aren't sourced, e.g. scp.

Upd

[root@reallin ~]# cat /etc/pam.d/su
#%PAM-1.0
auth            sufficient      pam_rootok.so
# Uncomment the following line to implicitly trust users in the "wheel" group.
#auth           sufficient      pam_wheel.so trust use_uid
# Uncomment the following line to require a user to be in the "wheel" group.
#auth           required        pam_wheel.so use_uid
auth            required        pam_unix.so
account         required        pam_unix.so
session         required        pam_unix.so
[root@reallin ~]# cat /etc/pam.d/su-l
#%PAM-1.0
auth            sufficient      pam_rootok.so
# Uncomment the following line to implicitly trust users in the "wheel" group.
#auth           sufficient      pam_wheel.so trust use_uid
# Uncomment the following line to require a user to be in the "wheel" group.
#auth           required        pam_wheel.so use_uid
auth            required        pam_unix.so
account         required        pam_unix.so
session         required        pam_unix.so

Answer 1

Although su -l <user> works fine on my system, I noticed that sudo su -l <user> – although it picks up ".profile" just fine – seemed to cause the same problem you describe of clearing variables supposedly set universally in "/etc/environment".

I was able to get what appeared to be a full login (execution of the ".profile" of <user> plus the variables from "/etc/environment") by doing:

sudo -i -u <user>