It's a combination of reasons, there is little precipitation in Antarctica so they don't get covered by snow and ice, likewise no vegetation to hide them. Most meteorites are black so they really stand out on the ice. (Similarly, the North African desert is a good meteorite hunting site because the meteorites sit on the surface for thousands of years).
If you're doing a magnetic survey, iron and stony-iron meteorites will be immediately visible to the sensors. Finally, those that do eventually get covered by the ice are transported to ablation zones where the ice sublimes and melts leaving meteorites behind, so you can get enormous concentrations of meteoritic rock at the toe of glaciers.