Vmca and Vmcg
There is no fixed and direct relationship between these because they occur under different aerodynamic conditions with no single, simple, factor dominating. The only true answer to your question, without delving into the minatuae of Boeing's aerodynamic and systems data, is "because it is".
What some airlines like to use as interview questions, they are welcome to use. But the fact that the interviewer expects you to say the moon is made of blue cheese, and everyone is therefore coached to say the moon is made of blue cheese, in no way relates to the composition of lunar rocks. For that I'd want to talk to one (or several) lunar "geologists".
EAS is "Equivalent Air Speed" and is commonly used for e.g. loads calculations, where the fact that the kinetic pressure is the same at all altitudes for the same EAS is very convenient.