If you are using the Smart system this is because activity bites  are set to "Not Used" by default as it is encouraged to not eat your activity points. If you would like to change that so that you do use your activity points then take the following steps:

  1. Go the Settings Tab
  2. Tap App Preferences
  3. Tap Activity Allowances
  4. Set it to use Activity Daily or Weekly depending on which you prefer