Maybe it's good for GitHub, GitLab, etc. to be as open and liberal as possible with its definition of open source, but I think there is definitely an argument to be made that businesses making source available without actually open-sourcing it should pay to have it hosted. GitHub didn't become proactive about asking users to add licenses to repos until far into its existence, and there's plenty of code there that doesn't have an explicit license, but I think participating in the open source community should actually require that your source is open. License proliferation is already an issue, but adding non-open source to GitHub seems especially dangerous to me. The license should be highlighted in bright red with a big note saying that users are not allowed to do what they will with the source code.