The space force exists so some lanyards can put "did x to help establish Space Force" on their resumes and some space command guys can say they work for a new branch instead of for the air force. The imperial bureaucracy is just a bunch of people with degrees giving each other jobs. The space people wanted to feel more important and saw Trump as an opportunity. Creating the space force let both Trump and the space people feel good about themselves, and the people in the military who might have opposed it were ignored by Trump because Trump thought the space force was cool.