I have an idiotic number of GitHub repositories. There are, at the time of
writing, 536 repositories in my account, of which I'm the "source" for
454 of those. At last count, I'm maintaining 159 of my own projects,
plus less-than-a-hundred-but-more-than-ten open source and closed source
projects for third parties.
When I registered on GitHub back in something like 2011, there was no concept of an "organization". People had personal accounts and that was that.
GitHub exposes many configuration methods that can be applied on a per-organization basis. For example, if a CI process requires access to secrets, those secrets can be configured in a single place and shared across all builds in an organization. If the same CI process is used in a personal account, the secrets it uses have to be configured in every repository that use the CI process. This is obviously unmaintainable.
I've decided to finally set up an organization, and I'll be transferring actively maintained ongoing projects there.