This is not specific to PackageMaker, this is a consequence of using GithubPagesForGAP. And, well, all those people did contribute.... But If it bothers you, you can discard the gh-pages history and start a fresh one, re-importing all files currently in there.

I would even like it to see the contributors per branch, especially for the gh-pages branch which plays a different role.

The motivation for writing this issue was that I was really puzzled to see Pedro and Chris on the list of contributors as I forgot about the gh-pages branch and expected this to be a GitHub error (I expect to see you everywhere 😄). Even worse, if one clicks on the contributor's link there is no reference to them anymore and there is no option to change the branch. I expect this to puzzle other people as well since they won't have the gh-pages branch on their minds.

... you can discard the gh-pages history and start a fresh one, re-importing all files currently in there.

I did this for the other packages but it is still persistent for CatReps, even though I recreated the gh-pages branch and force-pushed.

The acknowledgment for GitHubPagesForGAP is properly displayed on the bottom left corner here and I am happy with it. By clicking on the link one sees the corresponding list of contributors.

I just wanted to draw your attention to this issue and you are free to close it.

It is unclear to me what you are asking for, then. This sounds more like an issue with GitHub than with PackageMaker?