The fleet slowed down after a time.
There were several reasons why the ships needed to move slower.
First, navigating through an asteroid belt was quite perilous to say the least. The Gemini Family and the rest of the coalition did not dare to send too many of their starships through the densest areas of the belt.
Perhaps the scouting vessels and the smaller combat carriers possessed the agility to maneuver around the floating rocks, but the biggest and slowest capital ships were not as endowed!
The journey presented an especially serious danger to the fleets with a significant number of civilian vessels. The Larkinson Clan and the Boojay Family were especially reluctant to dive into the middle of the belt for this reason.