The problem that they have (and other user content created sites) if indexing was on is that SEO spammers use it to dump lots of links to sites.

That you don't see this is an indication that it works and dissuading those spammers.

Consider all the nearly forgotten repos out there that you occasionally stumble over and that there are no "work from home and get $30/hour - click here" or a dozen forms of "somespam.example.com" links peppering it.

Compare that with the old Wordpress blogs out there that haven't disabled comments and yet still have search indexing (or not, but spammers don't always dig far enough to see if there's a nofollow attribute on links).

So, for the most part, GitHub isn't indexed by search engines - and its across the board for the entirety of the site. Spammers realize that it is pointless to attempt in any of the forms that they could on other user created content sites and so expend no effort at all to post spam links.

Github discussions is searchable within GitHub in that repo. For example https://github.com/laravel/framework/discussions?discussions...

The wiki is fairly useful - and again, if you are searching for content in GitHub you can search wikis ( https://docs.github.com/en/search-github/searching-on-github... ) and get only content within GitHub (without having to sift through Google search results) with arguably a more powerful query language than Google's search bar ( https://docs.github.com/en/search-github/getting-started-wit... )

Personally, if I am looking for content for a FOSS that is hosted on GitHub I use GitHub's search for discussions and wikis first before trying to search for content in google.