How do you guys keep this game fun?

I love this game but I always find myself struggling with no objective. Career mode is annoying due to the random contracts and how they become obsessed with one planet at a time. I more like science mode, however I’m finding myself blowing through the tech tree, knowing that once I complete it I’ll probably get bored and want to start all over again. My thing is I wanna keep a save for a long time, building up huge colonies and relay networks. How do you guys keep yourselves coming back to one save?