Some of it was the latter. Matrix servers could be used in the past to store and serve unauthenticated media to anyone[0], which was described by the team as "not great"[1] and "abuse of Matrix as a content distribution network" [2].

I believe the team was prudent in being reserved about describing the issue (and the abuse it could entail) until after these changes rolled out in 2024[1], especially due to the unique challenges they required (including putting a freeze on unauthenticated media as part of the upgrade process).

[0]: https://matrix.org/blog/2024/06/26/sunsetting-unauthenticate...

[1]: https://2024.matrix.org/documents/talk_slides/LAB4%202024-09...

[2]: https://matrix.org/blog/2025/02/building-a-safer-matrix/

[3]: https://matrix.org/blog/2024/06/20/matrix-v1.11-release/

Former, I think. It involved highlighting all users of the room, and sometimes verbal abuse against Matrix and/or the projects which the rooms in question belogned to. Now that sort of abuse is much harder, since they have improved spam filtering.

Also not unheard of less ethical competitors to engage in such campaigns.