We're using unfed sourdough starter in these biscuits, which by definition isn't active and bubbly. That means the yeast in the starter isn't going help the dough expand, so you need to use a leavening agent like baking powder or baking soda in the dough. If you're interested in what happens to your dough when you don't use a leavening agent, I once made that mistake while baking some scones. Check out the FAQs for my basic cream scones to see the results.