Why are f-block elements placed below the main table?

Explanation

To accommodate the d-block elements the s-block and p-block elements are separated. There remains a gap between the s-block and p-block elements in the 2nd and 3rd periods.
If the f-block elements have to be accommodated in the periodic table again the size of the periodic table should be increased by separating the s-block and p-block.Then the table looks awkward. To avoid this the f-block element are placed below the main table.