Though there are a handful of potential reasons why the rolls are not fluffy, the most common are that too much flour was added to the dough or enough time wasn't given to let the dough rise properly. The bread will become dense, heavy, and dry if too much flour is added to the dough while kneading. To prevent this, add the flour to the kneading surface in small amounts, allowing the flour to be worked in before determining if you need more flour. Secondly, if the dough doesn't rise enough, the dough will be dense instead of light and fluffy. Allow the buns to double in size before placing them in the oven. A trick to know that they have risen sufficiently is to take a before photo to which you can compare the risen buns.