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.