After the prank. James and Remus have basically stopped all contact with everyone except from peter and lily and that drove Sirius crazy that he was being excluded so he started taking his anger out on the Slytherins causing regulus to, like Remus, almost get killed. Minerva decided the only way she was going to get them to talk was to set them up in this group chat and ban them from everything else, including going to class, until they had all become friends. Eventually they all got so bored they had to start texting on the group chat.