Why does the Electromagnetic force not dominate if it is much stronger than the Gravitational
force?
Simple: electric charge comes in positive and negative versions. Unlike charges attract; like charge repel. So all the positive & negative particles tend to pair up into neutral atoms etc.
Mass only comes in one type: positive; and all masses attract.
So as you pile up more and more electrically neutral matter, the gravitational attraction just keeps getting stronger, while the electromagnetic interactions stay cancelled
hope it helps friend