Comment 9 for bug 1613949

I suspect you don't have -updates enabled for universe in your /etc/apt/sources.list file. If you did you'd see the following:

 $ apt-cache policy vim-gtk3
vim-gtk3:
  Installed: (none)
  Candidate: 2:7.4.1689-3ubuntu1.1
  Version table:
     2:7.4.1689-3ubuntu1.1 500
        500 http://192.168.10.7/ubuntu xenial-updates/universe amd64 Packages
     2:7.4.1689-3ubuntu1 500
        500 http://192.168.10.7/ubuntu xenial/universe amd64 Packages

vim-common and vim-runtime are in main and you seem to have -updates enabled for that pocket.