Question

Why does the weaker force of gravity dominate over electrical forces for astronomical objects?​

Answer 1

Forces of gravity depend on quantities of mass, whereas electrical forces depend on quantities of net charge.

If gravitational forces dominate over electrical forces, it can only be because the amounts of net charge involved are much much much much much smaller than the amounts of mass involved.

What I'm saying is ... this doesn't mean that there aren't huge amounts of electric charge present in stars, planets, comets, and other astronomical objects.  But most of the charges are BALANCED ... there are equal amounts of positive and negative charge present in the same object, and there's very little of either kind left over, to be attracted or repelled by other objects.