As your course list grows, Canvas will attempt to determine which courses you use most often and most recently, and add those to your dashboard. In some cases, this will result in a course not displaying on the Dashboard's card view.
To explicitly set your preferences:
Click on Courses
A list of courses will open from the left side of the screen. Scroll down and click "All Courses"
Click the star next to the courses you want favorited - these will display on your dashboard's card view.