There's also the issue that some galaxies don't violate our pre-dark-matter models as much or do so in a different way. With dark matter that's easily explained

There's also the issue that some galaxies don't violate our pre-dark-matter models as much or do so in a different way. With dark matter that's easily explained as an abnormal dark matter halo (eg maybe displaced due to an ongoing interaction with another galaxy or absent for an unknown reason). When abnormalities like that are considered, dark matter becomes the elegant solution while theories that tweak gravity start to seem somewhat ad hoc.