I created a new App in AppStoreConnect and set subscriptions informations for it. Then
In the same project, when I used the same way to create other StoreKit Configuration Files which were synced with the Apps I already released, they showed correct IAP information.
It is so confusing. I googled but did not find any similar case. Any hint would be appreciated!
Solved!
The key is the subscription status should be "Ready to Submit" but mine is "Missing Metadata". I filled up all necessary items but did not upload a screenshot, so the status is still "Missing Metadata". After I uploaded a screenshot, the status changed to "Ready to Submit". And I finally can sync my StoreKit Configuration file now.