That's being enforced by libpwquality
and cracklib
which are used by gnome-control-center
to assess password quality. You can override it here: /etc/security/pwquality.conf
by setting dictcheck = 0
.
We will not be changing the default, however. Solus is a curated distro and we agree with the default settings as being sane for most use-cases, especially given that many installs are for laptops that may or may not be taken onto public networks. You are free to override it yourself, understanding the risks and the constraints of your limited use-case.