The appeal of modified gravity lies in all the observations Sabine outlines here, that don't fit our understanding. You need something to explain them, and the

The appeal of modified gravity lies in all the observations Sabine outlines here, that don't fit our understanding. You need something to explain them, and the choice is either positing lots of invisible stuff, or modifying the laws of gravity. It seems reasonable to try both approaches, particularly since positing lots of invisible stuff has a pretty checkered history in science.