The .NET Foundation asked for owner access on the author's repository (for a CLA bot). The author declined and a workaround was organized.
Years later the .NET Foundation asked for "owner access" on the author's repository (to allow them enforce Code of Conduct across all repositories). The author declined.
The CLA bot stopped working. The author was told it would work if he gave it owner access. The author was annoyed because they previously had a workaround. They gave in and gave @dnfadmin owner access (temporarily, it was later revoked after the CLA bot was set up, thanks /u/ethbr0 for the correction).
Some time later the author realized that the project had now been silently moved to GitHub Enterprise (likely in the short window @dnfadmin had owner access). The author states that projects in GitHub Enterprise can be entirely controlled by the owner of the account (the .NET Foundation). This transfer happened silently.
Independently, this happened to another project (who had coincidentally had an issue with a Microsoft employee and former contributor force a pull-request into their project: https://github.com/reactiveui/splat/pull/778). The change itself seems innocuous, but the approach bothered people.
People are upset because of how tone-deaf all of this is. They would like the .NET Foundation to stop trying to gain complete control over the member projects. They would especially like for their projects not to have their ownership changed silently.
Edit: For the record, I do not believe this is part of some embrace, extend, extinguish plan on behalf of Microsoft. I think these accusations actually cheapen what has happened here. I suspect this was more of a "can we make this process easier and more convenient for the .NET Foundation"-type thing.
The people involved with this will have to do some soul searching. The .NET Foundation should operate in service of its member projects, not the other way around.