I play solo mainly as it increases the immersion of being in the game world. Also it depends on whether I have time to be semi afk doing stuff but also interacting in real life. Additionally there is nothing worse than playing a space combat game with a party member playing metal over their mic, or shouting to other people whilst on mic, or speed running/tortoiseing a mission. Solo means I can do things at my speed in my own way. I also play with a small group of friends, and we do all aspects of the game together. But we all like time solo playing too.