To insert a row BELOW the currently selected row in Excel, you can follow these steps:

1. Select the row below where you want to insert the new row.
2. Right-click on the selected row and choose "Insert" from the context menu.
3. In the "Insert" dialog box, select "Entire row" and click "OK".

Alternatively, you can use the "Insert" button on the Home ribbon, as you mentioned, but make sure to select "Insert Sheet Rows" instead of "Insert Sheet Columns". This will insert a new row BELOW the currently selected row.

As for why the "Insert Rows Below" option disappeared from the Table menu, it's possible that it was removed in newer versions of Excel to streamline the user interface. However, the above methods should still allow you to insert a row below the selected row.