Because a lot went down:

Eva and Ariadne secretly tried to assassinate Plutarch during the crowning ceremony in a misguded attempt at rebellion. Then Eva ratted Ariadne out publicly.

The bomb went off, but Plutarch was not injured. However, Ariadne is currently prisoner of the Capitol.

As soon as this happened, Peacekeepers escorted all Tributes back to their District Suite, where they will be confined until further notice. They are not being allowed to move between Districts, but can still contacted each other on their communication devices, publicly and privately. They also can mingle within their District.

If you have already done something inter district, don 't worry, just feel free to NPC a peacekeeper coming to round up the loose Tributes post haste.