Rules
They started off extremely benign to the point that many relaxed. Maybe they were overthinking things and this sudden rule change was only really a method of making sure they stayed in line.
In the past, even with rules there, with the only real punishment being confinement, many terrible people would flout them and accept the jail time. Considering they would be released for their matches, and would obviously be released after the Gathering ended, why should they care?
There were a fair share of the weak that had been directly killed for offending the wrong people or even looking at them the wrong way. The worst part was that often the people they had offended wouldn't even act themselves. Instead, they would pay someone else to do it and take the jail time for them. Sometimes it was life-changing money on the table, so who wouldn't jump at the chance if the only punishment was staring at four walls for a bit?