It's not, though. Git is a means of distributing content, not the content itself. The thing analogous to PornHub's porn on GitHub is the source code in the repos hosted there, not Git itself.
Git is a DVCS. GitHub is a place where DVCS repositories are hosted. There are many other places where DVCS repositories can be hosted, but GitHub is the most famous one.. Porn is a type of content. PornHub is a place where porn is hosted. There are many other places where porn can be hosted, but PornHub is the most famous one. It's a pretty good analogy.
Sure... and you could pass around porn on thumb drives. But, having a central website where you can browse public repos and clone the interesting ones is a pretty key part of Open Source / Free Software development.
How many people use Github for discovery though? I usually find interesting projects through a search engine, through word of mouth, through posts on here, etc. at which point it doesn't really matter where the repo is hosted. A lot of the useful projects I use aren't even on Github.
As far as I know, Gitea is current working on federation support, which will be great. It'd be like Lemmy where you can browse repos, submit issues, etc from one instance even if the repo is hosted at a different one. Git was really designed for a model like that, not for a centralized one.
How many people use Pornhub for discovery though? I usually find interesting content through a search engine, through word of mouth, through posts on here, etc. at which point it doesn't really matter where the porn is hosted. A lot of the useful content I use aren't even on Pornhub.
Seriously though, I agree with you, githubs value to open source is not it's discover-ability. Personally I think its value comes from the stability, as much as I'm an advocate for self-hosting I know from the amount of dead links on the internet that we could have lost a lot of projects or at least they would move about as hosts went down.
I quite like the idea of federated gitea, although technically there is already a federated platform for porn if you count Lemmy and/or mastadon.
Depends on to whom. If you're explaining to your grandma, a small child, a co-worker, or a student under your tutelage, you probably don't want an explanation that relies on reference to a porn site.
And if you're explaining to a novice developer or to an IT person who sometimes might have to work with Git, they deserve an explanation that leaves them with a basic understanding (or at least the names) of the kinds of things Git and GitHub are (VCSes and SCM forges, respectively), not just an inkling that GitHub is not unique in being 'a place to host (some?) Git, whatever that is'.
So... if you don't mind that it suggests 'GitHub is for uploading Git(s)', that line is an okay way to teach 'the difference between Git and GitHub' to non-technical, non-elderly adults who don't really need to know what Git is (and don't work with you or study under you).
That's an explanation of pretty damn narrow usefulness, to put it generously.
I agree that porn is a nsfw way to explain something in a lot of scenarios but I disagree about people needing to know at least the names of a technology from an explanation.
Most people don't need to know or care about the names to understand or use them. Knowing the names after I learnt the commands did not give me greater insight into how the tool works.
If they are just being introduced to git and github then they are likely new to programming and have much more important things to care about like learning their first programming language or understanding how their teams project actually works.
A place to host gits is a perfectly good explanation for anyone who is new to it.
Not unreasonable. But consider: GitHub provides access to git repositories (the data), and git metadata is used to enrich the interactions with the underlying files (by showing the git history, linking commits and such). PornHub provides access to porn films (data) and uses porn metadata (tags, actors, etc) to enrich the user interaction (by providing relevant links and suggestions). Both GitHub and PornHub are services that enrich the underlying content data by using a metadata source.