These snickerdoodles are supposed to be on the flatter side but too flat means there was an issue. One, you may have used a low quality butter which has a higher water content and more fillers. Two, the dough was too soft by the time you baked the cookies. Avoid this by chilling the cinnamon sugar rolled cookie dough balls in the refrigerator for 15 minutes and immediately putting them in your oven. Three, try creaming together the butter and sugars longer next time (3-5 minutes will result in a thicker cookie).