Is there a reason why every component of gonum is scattered across different repositories. For me, it makes it extremely hard to browse through the stuff and try to find anything that might be useful to me.
You're more likely to touch more files if they are all in the same repository. All of the issues are going to be in the same issue tracker (tags can help, but only if you know how to use them well, and that causes overhead for the maintainers), and all of the Pull Requests are going to notify everyone who is watching the repository, whether it's relevant to the part you care about or not.
There are clear drawbacks, but there are clear advantages as well.
In the beginning we were still trying to figure out what we wanted. There was a lot of really free-form changes, and it was easier to keep those sweeping changes isolated from one another. We're planning to do a couple breaking changes at once at some point, and one of those is likely moving everything into a single repo.