The tiny ball also bends space-time, but the curvature is negligible compared to that made by the massive ball. Gravity works in a similar way. Although the other three fundamental forces play vital roles in a star, they are irrelevant when it comes to the scale of galaxies. This is because weak and strong nuclear forces are only short range forces. Their influence does not go beyond the nuclei of atoms.
Electromagnetic force is a long range force like gravity.
However, unlike gravity, it not only attracts but also repels depending on what charges are involved. Our universe seems to have an equal amount of positive and negative charges. Therefore, the attracting and repelling forces cancel each other out when they are spread out over a sufficiently large scale. Gravity acts like an organizer that puts stars, galaxies, and clusters in order.