puts his arm around everyone as an excuse to put his arm around daphne
puts his arm around members of his polycule
he just loves his friends a lot
Fred just enjoys sitting like that and the others take advantage for snuggle time
Fred has very wide shoulders, and if he kept his arms down at his sides he would take up a disproportionate amount of space, so he drapes them across the back of whatever he’s sitting on to be considerate to those around him. It’s the moral and philosophical opposite of manspreading.