Proprietary graphics drivers are not installed for GTX 980 Ti even when asked to do so during installation time on Mint 18

[juj]

STR:

1. On a system with GTX 980 Ti graphics card, perform a clean install of Linux Mint 18.
2. During installation, a dialog pops up asking "Install third-party software for graphics and Wi-Fi hardware, Flash, MP3 and other media". It looks like this: https://www.linuxliteos.com/manual/images/install/installwizard/install-ll2.png

Check that box to opt in.
3. Proceed with the installation while having a wired network connection open throughout the installation, and reboot when done

Observed:

When the system boots to desktop, a dialog pops up saying "Running in software rendering mode". The dialog looks like this: https://www.organicweb.com.au/wp-content/uploads/2014/09/Linux-Mint-Running-in-software-rendering-mode-error.png

Expected: The installer should have installed the proprietary third-party software for graphics hardware, like it offered to.

[juj (jujjyl)]

Also occurs when attempting to install Ubuntu 16.04 RTM.