I think it is something similar to when you spin something like a top. Momentum makes matter spread outward and flatten. Once things near the center start hitting each other and combining, that's when they form a sphere.
Not anon who posted, and it's been a long time since I've learned any astronomy. I remember wanting to research space, particularly black holes as a child. Wish I had the excitement for anything anymore.
Which leads me to my pape. I need help. I have no motivation.