No thats not a strange decision. self-hosted git servers disappear all the time, it's better to have everything unavailable at once when github is down than suffer whenever either of the sources goes unreachable. Non-developers view git availability as a simple utility, they don't attach a value judgement to git being usable with any remote.
> suffer whenever either of the sources goes unreachable
This is not the way Palomar works. From the About page (https://palomar-registry.org/about):
> Palomar does keep a public preservation fork of every registered source, solely as a backup for the registry in the event that the original repository disappears.
The decision to limit git sources to Github is likely in order to be able to use Github's fork mechanism. Palomar could still offer to take a copy of the relevant commit of non-Github repositories.
The main reason Github is in the news these days is due to its unreliability. If availability is your main concern, Github would be a very odd choice for your One Blessed Source.
Besides, it isn't "self-hosted basement Git server VS Github". There are plenty of other large and reliable forges out there, such as GitLab, Sourcehut, Bitbucket, or Codeberg. Considering how many people - from individual devs to major open-source projects - are abandoning Github, launching a new project in 2026 which only works with Github is a rather odd choice.
It doesn't even make sense from a technical perspective. Git has a standard protocol it uses for cloning repos. You have to go out of your way to make it not work with other forges. And if reliability is critical, surely you'd just mirror it locally? Heck, why not make use of Git's inherent distributed nature and allow defining multiple upstream sources? Integrity is already handled by the commit hash itself, so it doesn't matter if you fetch that commit from Github, GitLab, or some guy's basement server - just take whichever one happens to respond the fastest.