Why are cells small indeed? Well, it's really the physical and chemical laws that limit cell size. Substances need to move to and from cells and also within cells. If cells become big, it will take a long time for substances to move from one part of the cell to another and this will not be compatible with life. I have an actual table showing how far substances can move if the distance between the cell membrane and the cytoplasm is in nanometers or in millimeters. However, I cannot find the table right now. I promise I will post it sometime soon. As soon as I find it that is.
Suffice it to say for the moment that one should never expect to find a single cell that is as big as a basketball.