That's true of Amber Alerts everywhere. The purpose is to find a fleeing abductor right away. It also requires a basis to believe the child is in danger, so you would not usually see Amber Alerts in cases of a parent abduction, absent some known threat.
In those case then the parent had to have been deemed a threat. Maybe they lost custody due to having harmed the child before or for being unable to care for the child. Maybe they made threats to hurt the kid.
Not taking about statistical likelihoods. Amber Alerts say "this kid is not just missing, but in danger."