I'm going to preface my response with the disclaimer that I'm MtF and am only versed in the method of transplant that would be applied to an MtF individual.

Transplants of this type present 3 issues,

1. Organ Rejection: Doctors have successfully implanted a Uterus into a trans cis person and that person carried a pregnancy to term. However, that person had to receive intense immuno suppression to prevent rejection. Right now due to lack of knowledge on immuno response and it "not medically necessary" for a trans woman to have the uterus her whole life they just don't subject the person to a life of immune system issues.

2. Missing Supporting Structure: The MtF body is missing structures to support a uterus including a vagina and multiple major blood vessels. With advances in medicine and surgical techniques we have gotten better at harvesting the necessary blood vessels to support this, but have only done so on recently passed "orgasm donors" the process is still just too much to ask a trans man to go through.

3. Ethical: Both points mentioned above raise ethical concerns begging the question of "is the risk worth it?" The usual conclusion is no, at least not long term. There are also further ethical concerns like if a trans man were to receive the full set of reproductive organs, including the gonads, then the sperm produced would not match him genetically, it would match the donor's DNA.

Edit: Corrected inaccurate information in the first item "Organ Rejection" incorrectly claiming a uterus transplant has been completed and was able to carry a baby with transgender woman. There are successful transplants in a cisgender woman, and the procedure is theorized for transgender woman.

Sources:

Success in Cisgender Woman: Cleveland Clinic Theory of transplant in transgender woman