Why can’t I change the ad group level hierarchy of an existing ad group using the Restructure Shopping Campaigns tool?

The Restructure Shopping Campaigns tool doesn't change the ad group level hierarchy, as it would be the same as creating new ad groups. We don't change ad group levels because when doing so, you'd lose historical data and start with a fresh new ad group.

If you'd like to create a new ad group or campaign, please refer to the Shopping Campaign Builder tool.