Future humans will be part human, part lizard, part zebra fish, and seveal other species. We will regrow teeth, heart, and limbs. Sometimes we might accidentally grow a tail.
Because nothing comes without a cost. Maybe mutations that would allow us to regrow limbs also lead to horrific cancers that snuffed out any chance for reproduction. Maybe the benefit didn't outweigh the additional energy budget. Maybe it was just not necessary for procreation vs our advanced cognition so it never played into evolutionary fitness (compared to a lizard that can drop a tail when it's attacked, and regrow it for the neYt attack, which would surely improve its evolutionary fitness).
Additional reasons: our mammalian organs are highly complex, we live a long time, we are large animals with giant brains and high metabolic cost. The list goes on.
In some ways evolution is inevitable but it is also a stroke of luck. The mutation behind the phenotype needs to actually happen. Then the mutant individual needs to actually have outsized reproductive success such that their progeny outcompetes with others and these mutant alleles spread in the population.
