Why is the largest single cell organism only 5cm

Biologists used the world's largest single-celled organism, an aquatic alga called Caulerpa taxifolia, to study the nature of structure and form in plants. It is a single cell that can grow to a length of six to twelve inches.

The remaining cells can divide and make new cells to heal the wound. But an organism made of one large single cell will die from even a small wound, because the inside contents of its single cell will leak out and it has no backup cells to preserve its life therefore cells can't be that large in size.

Hope this helps!

thinking it would be physical characteristics