Why the default username is "user" , and password "changeme"
Because 'technically' there is "no installation". Whonix images are pre-installed operating system images. The history of Whonix is that we started to ship downloadable VM images. What you might perceive as installation process, for example VirtualBox import is "not an installation". It is the same for any VM image that would be imported. There is no feature in virtualizers that would allow to inject code to do things at this stage. The code running for importing the images is solely by the virtualizer and modifying that would be non-trivial and require to maintain a fork of the virtualizer. To add such code on the operating system that hosts Whonix would be non-trivial and operating system specific. It would require to mount and modify the images. Too unimportant to put any effort into it. Would probably result in more bugs, and confusion, than what we have now. I see Qubes(-Whonix) as the evolution of this, since there are no passwords there.
further discussion here:- https://forums.whonix.org/t/whonix-installation-from-default-password-to-user-password/2073/2
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