Why Whonix uses old kernel?

I am new in Whonix & linux in general. Could someone explain me why Whonix-Workstation uses old 3.* kernel?
Why not to upgrade to the current 4.* kernel?

Hi. Whonix 13 is based on Debian Jessie aka old-stable that uses an older/stable kernel. Its not a problem as Whonix runs in a VM and so hardware compatibility is not a factor.