Why was my theme extension app rejected from the AppStore?

[KevinKay]

Hello @Community ,

We have developed a Shopify theme with a lot of demos and an extension app to make it easy for users to import the demos in the theme. We want to publish this app to the AppStore so that users can install demos for their store. But we got a message review:

Required changes
Apps that allow merchants to install a theme to their store are not permitted on the Shopify app store. See the screencast for details. 

https://shopify.click/65746-8306-95675-47090-77453.webm

I saw a lot of page builder apps and another app in AppStore has that function. 

Could you help me a solution to resolve it so I can resubmit the app again?

I have read through the requirements Documentation but not found this case.

Thank you, 

Kevin