The answer is because we can't afford to wait that long.
Time is of the essence.
The logic of this argument suggests that in order to extend our lives, we should restore deficient hormone levels to their youthful physiological levels either by taking pills when possible or injections when necessary. However, we also realize that hormonal interventions are only a temporary stopgap measure until more permanent cellular revitalization is possible. The human species is still here after many hundreds of thousand of years on the Earth. A microscopic tissue pathologist or histologist would be pleased to point out the accumulated lipofuscin pigment and many other age-related changes associated with old cells. Rapidly dividing epithelial cells also undergo chromosomal changes in their nuclei related to telomere shortening.