Why does the paratially transplanted liver grow to full size not larger?

It can grow to full size as liver cells divide.
Ususally robust liver is not large (ie: it's not palpable).
[No doubt the transplant liver is stout liver.]
The same reason the ingenious liver grew to full size and not larger. The cells contained by the liver get signals from their environment (i.e. the rst of the organs oaround it) to permit the cells know whether it is appropriate to divide or not. When it reach the edge of the liver's "border" the cell sense this and stop dividing.
Genetic pre-programming!