Well if the small intestine needs to absorb the nutrients, then the nutrients kind of have to go somewhere right? also, there is a transfer from high to low inside the small intestine there are lots of nutrients that need to be absorbed to be made into energy the cells would only have to take in more nutrients if it has run out, aka it's low on nutrients thus the high concentration outside the cell and the low concentration inside leads to the active transport through the cell membrane
Though some cells are bigger than others, they do not scale with size. For example if you look at skin cells on a dog they would be similar in size to a skin cell from a human. When an animal or species is bigger it is usually just made from more cells.
