Ah, I was wondering the evolutionary reason why those genes would have gone dormant.

Cancer is a sensible answer.

Yep, the unfortunate flipside of "let's use stem cells to rebuild stuff" is always "let's use stem cells to give us cancer". Technology might help alleviate the cancer part compared to blind evolution, hopefully.

Teratomas are insane.

https://en.wikipedia.org/wiki/Teratoma

Some aging mechanisms like telomeres are also mechanisms to prevent cancer by limiting cell division.

It looks like one of the optimization edges walked by evolution is a conflict between longevity and the ability to repair and regenerate versus not getting cancer.

It’s easy to make human cell lines immortal, but that will kill you.

One route I can imagine to radical life extension is to start by editing the genome to introduce much more robust but different anti cancer adaptations. Then start turning regenerative stuff and things like telomerase back on.