Because of the library dependencies and their respective versions. But Kicad 4.0.5 is readily available in the 'backports' branch for the stable release: https://packages.debian.org/jessie-backports/kicad
My guess is: Same as with Debian stable, Linux Mint 16 could simply be too old (it was released in 2013), i.e. the libraries Kicad 4.x depends on are not available with the required versions.
@Harald_Hoopmann: With Linux Mint 18.1, Kicad 4.0.5 is available from the Mint package repositories.
Another possibility (without any guarantee for the outcome) is to unpack the .deb-file for Kicad, manipulate the configuration file containing the dependencies and change the required versions for the libraries to those available on your system, repack the .deb-file and install it manually with dpkg. I've done this a few times, but would not use this way for 'mission critical' and production systems unless thorough test haven proven the stability.
It might be easier to back up your whole system and try an upgrade to a newer version of Mint. I'm sure Kicad is not the only software lagging behind on a Mint 16 installation.
Edit: If you are inclined to hang on to your Mint 16 installation, you could also try and pull the kicad and kicad-common backport packages from here https://packages.debian.org/jessie-backports/kicad and here https://packages.debian.org/jessie-backports/kicad-common (see bottom of the pages for the different 32 Bit / 64 Bit and architecture builds). After download try installing them with root/superuser rights with 'su dpkg -i ./package_name'. This may or may not work (Debian stable still is roughly 1 1/2 years younger than Mint 16, but since Debian is more 'conservative' there may be a chance that it has the correct library versions and this works out).