Because the expiration date has been reached and the signatory has not signed. You must resend it  if  the signatory is willing to sign.  

The expiration time of a contract is  defined in the settings of the template. You can check at "My templates" section at the "Expiration Time" column.

By clicking on  “Sent List” > “Expiration Date” you can check  the expiration date.

Furthermore, the expired sending list can be consulted in the “Sent List”, > “Status” “Expired” (see question 2) between a time interval with date and time.