It is related to the shape of these orbitals, but importantly, also with spin-orbit coupling. Two electrons in one orbital must have spin directions opposite to one another. There is no spin-orbit coupling in s-orbital, so these electrons repel only because of their charge. The electrons in d-orbital share a common direction of magnetic field to align relative to. Given that their preferred positions relative to the non-spherical shape of d-orbital and each other are near opposite ends along the direction of the magnetic field, their spin magnetic moments being opposite contributes to repulsion.