When we receive a flag on an old question, we typically ask the moderators of the target site if migrating it would be appropriate. A question might not get migrated because:
- It is too old, and duplicates existing content
- It is a 'list of' or 'what's best' question, or otherwise too subjective to send
Additionally, we don't typically migrate 'famous' questions to sites that are not yet out of beta. While most SE sites do eventually launch, there is always the possibility that they might run out of steam. I realize that the Apple SE site has launched, I'm just listing reasons why we might decide not to send it.
We do appreciate the flags that help churn these up to the top so that they get attention, but we can't always subsequently migrate them.
An example of why we're rather cautious can be seen in the toilet bowl incident.