Probably it's because the secondary data source didn't return more than one when you configured it. Look at the data source and select the secondary data source from the dropdown. If the control is not repeating, that's an indication that the "schema inference" failed to think it was repeating the first time you connected to it. This could be because you entered a value in the data connection wizard that only returned one row. To fix, just go to the data connections dialog and modify the data connection and make sure that you don't enter a filter.
Another issue could be that you are trying to copy repeating items into the table. To do this requires having blank default values in the main data source, or using qRules insert command. We have documentation on this and have done webinars showing both techniques.
Please let us know which issue it is.
Thanks!