Duh, wasn't that a large part of the reason they survived? Cause lots of them were underground dwellers?

Uhm, yeah? As well as all the 150 million years before?

Toward the end of the Cretaceous, flowering plants (angiosperms) transformed ground habitats, making them more diverse. While it was known that tree-dwelling mammals faced challenges after the impact of the asteroid, it wasn’t clear if mammals adapted by becoming more ground-based. Earlier research primarily analyzed complete skeletons to study how ancient mammals moved.

A recent University of Bristol study reveals that many mammals were transitioning to a ground-based lifestyle before the asteroid’s impact. By analyzing small bone fragments—an approach never used to study whole communities—the researchers examined fossils from museums in New York, California, and Calgary. Their findings show that a significant shift toward ground-dwelling occurred several million years before the mass extinction that ended the age of dinosaurs.