Symbol of Authority
What was a crown?
In ancient times, it was a fancy way of denoting authority. Anyone who wore an elaborate metal band on the head would instantly be recognized as the one in charge.
Over the ages, the tradition of rulers wearing crowns became so strong that their association with power, authority and rights had become ingrained in the human consciousness!
Crown = ruler.
Though monarchies suffered a decline as people no longer took the divine right of kings seriously, they underwent a revival after humanity spread across the stars.
Many wealthy groups and individuals that invested so much into setting up colonies in distant planets wanted to enshrine their right to rule in a way that was compatible with inheritance.