Winamp had a bunch of other issues with code they didn’t own being stuck in that repo. Github encourages FOSS licenses, but doesn’t require it.

https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/licensing-a-repository

You’re under no obligation to choose a license. However, without a license, the default copyright laws apply, meaning that you retain all rights to your source code and no one may reproduce, distribute, or create derivative works from your work.

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If you publish your source code in a public repository on GitHub, according to the Terms of Service, other users of GitHub.com have the right to view and fork your repository. If you have already created a repository and no longer want users to have access to the repository, you can make the repository private. When you change the visibility of a repository to private, existing forks or local copies created by other users will still exist. For more information, see “Setting repository visibility.”