Limitation of HUB:
If multiple systems are trying to send data at the same period of time, the electrical pulse sent across the cable can interfere with each other. So, the connection ultimately slows down and hence switches came into existence.
So, the limitation on the number of hub sites is not restricted because of the ‘role’ of the site but a decision by Microsoft to cap this number. Different organisations may find the limit problem free but many, particularly larger organisations may hit issues.