The reasons for this change seem to be described in [0] with the following summary:
> The contribution workflow in Guix has been facing several challenges:
> difficult onboarding, lack of legibility, complex, unreliable, and
> labor-intensive infrastructure, and lack of automation. All these lead
> to an experience that contributors often find frustrating and hinders
> quality assurance efforts. We propose to address these limitations by
> migrating repositories, issue tracking, and patch tracking to Codeberg,
> an integrated forge with a Web interface that is hosted by a non-profit.
The reasons for this change seem to be described in [0] with the following summary:
[0] https://archive.softwareheritage.org/browse/content/sha1_git...They were still on savannah only. OMG.