Can head transplantation to artificial body be the best option?

If we think we have multi-organ support system developed enough to support life in isolated head,
why can't that system support life in the head + body? Why do you want to separate head?

Possible convincing answers:

• We want to isolate brain from metastatic cancer cells.

Possible not convincing answers:

• Supporting life in head might theoretically be easier or cheaper because head weights just ~8% of the body weight (though brain consumes ~20% energy). Sounds not really convincing.
• We can support life in whole body but want to isolate brain from some bad factors in the blood which accelerate brain aging. Ok but there are other ways to combat those factors: plasma dilution, antibodies or other drugs to blok those factors.

Heart failure

Let's suppose the patient is dying of heart disease.
What is wiser to choose: standard ECMO or head transplantation?
Standard ECMO is a well tested method which can support life for several weeks bridging patient to heart transplantation (or to artificial heart).
So probably ECMO would be chosen. Only if ECMO fails it probably could be wise to try head transplantation.
However if ECMO failed to support life in body why it would succeed to support life in isolated head?

Cancer

"from 10% to 26% of patients who die from their cancer will develop brain metastases" https://www.ncbi.nlm.nih.gov/books/NBK470246/
"The incidence is 9%-17% based on various studies, although the exact incidence is thought to be higher. The incidence is increasing with the availability of improved imaging techniques which aid early diagnosis, and effective systemic treatment regimens which prolong life, thus allowing cancer to disseminate to the brain" https://pubmed.ncbi.nlm.nih.gov/22012633/
So there is some chance that when person is dying of cancer there are already metastases in the brain so head transplantation probably wouldn't help. Anyway in most of cases there probably would not be any brain metastases or they will be too small/unimportant to influence life expectancy.