Please post your question on
https://discuss.gohugo.io/ instead, as all the discussions are happening there, whereas this particular mailing list or Google group is not well attended if I understand correctly.
Anyhow, to answer your question: Good question! I have wondered about the same question myself. I suppose that some site owners do not want to share the source code to their website, for whatever reasons. It is not ideal, but some of the sites-without-source are interesting nonetheless and was thus accepted.
Cheers,
Anthony