The cloud that became a cluster was probably denser initially. No star-formation going on even back then in elliptical galaxies. This means that star-formation ended for elliptical galaxies even when they were very young. Other evidence around but too much to go into. The complication is that galaxies interact .
Stars are very far apart, compared to their size.
Galaxies are not. Distances between galaxies are more comparable to their sizes. When the universe was younger, it was smaller, so more galactic collisions happened. Use computer models to see what would happen. Disks torn apart, making orbits more random.