There isn't currently any other way to add a new row when building a page. If you would like to see this as a future feature on Igloo, please submit your idea to our Product Zone page here.
I see that this feature has already been requested: CARE-I-533. It will be reviewed by our Product Team for consideration of adding it to the platform.
In the meantime, I have found the process is slightly easier if you first drag the widget to the bottom of the existing row, and then drag it onto the bottom line to create the new row. See the attached GIF for example.