Then it no longer belongs to you, so no freebie. You are taking land that you have previously admitted is not yours.
Its not about that, it is about the 'free claims' you get whenever forming a certain country.
The way AE works + OE + lack of admin power for coring, you often are unable to get all the provinces on time.
The fact that they are not cores is already harsh enough, but this way at least you will be able to get provinces later, core them easier, and all with legitimate reasons namely them belonging to your primary accepted culture group.