Like most religious practices, reincarnation doesn’t work unless you truly believe in it. Humanity is special, as unlikely as that may seem at times, and if they believed in something, that would change reality.
And the reality this time was at a turning point. The coming years would be challenging, and it needed a leader for the faithful with just the right mix of intelligence, charisma and faith. Luckily, just as the last leader was dying, such a young boy was being born, and he’d secure their faith for generations.
Shame that the doctor pulled the other twin out first.