nm-applet is in the "RequiredComponents" of /usr/share/cinnamon-session/sessions/cinnamon{,2d}.session. ( See https://github.com/linuxmint/Cinnamon/blob/2.6.13/files/usr/share/cinnamon-session/sessions/cinnamon.session ) But users who prefer USE="-networkmanager" do not use nm-applet in Cinnamon. Indeed, this inconsistency is harmless. Because cinnamon-control-center's ebuilds has nm-applet dependency, there is nm-applet in the system. But the users don't want to run nm-applet. Also, most of them don't run NetworkManager, so nm-applet is needless. (And, if someone changes cinnamon-control-center to add IUSE="-networkmanager" and drop networkmanager and nm-applet deps, this will become a harm.) Reproducible: Always
A proposed ebuild for this already exists on #553946.
*** This bug has been marked as a duplicate of bug 553946 ***