(MC POV)
Surprisingly, they actually did put all the sacrifices together in one giant hall.
I had half expected each of them to have their own separate cell to be locked up in, just in case to avoid the sacrifices colluding together to work against their captors.
But it seems like they have some form of Quark inhibitor inscription laid around the area that severely limits the usage of Quarks.
Any Technique that a Practitioner tries to materialise will be absorbed and dispersed by the inscription, destroying the Technique even before it can be manifested.
Normal Practitioners probably wouldn't be able to use any Techniques while inside this inscription, which is most likely why they aren't worried about the prisoners banding together. With the thick stone walls and the steel reinforced doors, no normal mortal can get out of here easily even if they grouped together.
