I am not sure what you did during the publishing of your workbook to Tableau Server there might be few cases due the same your workbook is not getting refreshed.
1. Have you changed the below setting below publishing the workbook to server.
As per the above screen shot if I will not allow authentication from "Refresh not enabled" to "Allow all access" then server will never refresh your data thou you have enabled the scheduler for your workbook.
2. Or there might be reason your Tableau server is unable to reach to your SQL Server if above option is set to "Allow all access" in this case as will data will never be refreshed on the server.
Is your Tableau server is in the same network where your SQL server is.
Or share the exact error of the extract failure so that I can help you in fixing the same.