Applications folder not owned by root, cannot change it
Funnily enough this is a perfect example of one of the few situations where repairing disk permissions is actually called for.

Unfortunately the Repair Disk Permissions option has been removed from Disk Utility in El Capitan.

However you can still do it from the command line.

In Terminal run the following command to find out which permissions are incorrect.


  sudo /usr/libexec/repair_packages --verify --standard-pkgs /


And run the following command to repair the permissions.


  sudo /usr/libexec/repair_packages --repair --standard-pkgs --volume /


More information here: http://osxdaily.com/2015/11/04/verify-repair-permissions-mac-os-x/