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.
Under the state’s Amber Alert program, missing children must be 17 or younger and in danger of serious bodily harm or death, and there must be enough “descriptive information about the child, the suspect, and/or the suspect vehicle to believe an immediate broadcast alert will help locate the child,” according to the Justice Department’s website.
Johnson said she believes the Justice Department may have denied the request because there was no suspect description or vehicle involved when Prince disappeared.
If we start getting Amber alerts for every single missing child and most of them don't contain any information we can actually use to help more and more people are just going to click through the alerts without even bothering to read them.