Each AWS service may choose different pipeline ordering based on the risks specific to their architecture.

In general:

You don't deploy to the largest region first because of the large blast radius.

You may not want to deploy to the largest region last because then if there's an issue that only shows up at that scale you may need to roll every single region back (divergent code across regions is generally avoided as much as possible).

A middle ground is to deploy to the largest region second or third.