It's rare because almost all kidnappings and other harmful things done to children are done by people who aren't strangers:

Aunts and uncles, parents, coaches, family friends, community leaders, religious leaders, day care employees, etc

They never seem to even acknowledge that, let alone care about fixing it.

This was known from the statistics even before these people insisted every school teach children about "Stranger danger" because these specific people are utterly incapable of overriding primal fear, fed by "news" they insist on watching, with factual reality.