However, Linux and FreeBSD are Open Source and more friendly for Community participation. So you are welcome to write an installer for FreeBSD/TrueNAS.
We already have an installer for Linux (Debian-based): [Tech Preview] Linux Installer Part 2
The main problem of other OSes - no uniform installer, even within a Linux ecosystem there are at least two major package systems (but in reality - any distro have an own implementation). This is a nightmare to support all of them.