Why are my apps not working with subscriptions?

Apple won't merge accounts. That has never been possible. You can do various things yourself that will 90% get that far but those are not things Apple will do for you.

Was this what Apple did? --> Migrate purchases from one Apple Account to another Apple Account - Apple Support

An Apple account is defined by a single email address. If you have two addresses, you have two Apple accounts. You can't have two addresses linked to a single account unless the second one is simply a notification address and not used to actually identify an account. If you have two Apple accounts, Apple will tell you that you cannot merge them. They may or may not mention purchase migration.

Also note that some vendors let you set up subscriptions directly with the vendor. If that is the case, they won't appear in your purchase history because they have nothing to do with Apple.

I am just another customer like you and I don't have Apple's resources to investigate these items for you. All I have to go by is what you say, and hence my confusion when you talked about combining accounts. Items purchased with one account are permanently identified as belonging to that account. You might be able to share them with Family Sharing if you cannot or do not want to migrate them to a different account.