Because anyone can upload illegal images without the admin knowing and the admin will be liable for it.

The admin/company isn’t liable until it is reported to them and they don’t do anything about it… That’s how all social media sites work, Google isn’t immediately liable if you upload illegal materials to GDrive and share it anonymously.

They do plan to switch to the x.com domain and already own it.

Exactly, Threads will use the Fediverse to seed content and then start to drift from the standard when they have sufficient user base that they don’t need the outside content. They will start to shift all communities to be Meta-hosted and stop advertising the others. Eventually they will just disconnect entirely.