Why can't a uterus be transplanted just like a kidney or a heart?

A uterus transplant has been successfully performed (meaning someone did get pregnant and have a healthy child from it), however since a uterus is not necessary to prolong a patient's life (unlike a heart, liver etc...) they are not commonly transplanted since risks would outweigh benefits.

As with any type of transplant, anti-rejection medication is necessary to help ensure graft survival. The problem is, anti-rejection medication is not a great thing to be on during pregnancy due to the potential side-effects it may have on a developing fetus. This in turn makes uterine transplants "unnecessarily risky", especially since the same result could be achieved more easily using a healthy surrogate mother.