Much speculation has been made about the possibility of Earthlike Moons around Giant planets in a stars habitable zone. I have to wonder if this is possible based on limited empirical evidence however. Why are the large moons in our system limited to Mercury's size. While Jupiter's satellite system masses far more than Saturn's as you would expect from its higher mass, it simply has more Mecury and Luna class moons than saturn rather than a much larger top Moon.

Does anyone have planetary formation modeling insight into this? Is this just a fluke, or is there some forces that tend to constrain a Moons upper size?

Regards,
Mark