Hey @CornDontCare,
Linking your platforms from a different EA account will cause progress to be lost as you've found. Progress is stored on the EA account level, not on individual platforms like PlayStation, Xbox, Steam, etc. This means if you link your platform to a different EA account, you'll lose access to that progress.
In this case, you've just linked Steam and Xbox accounts to your current EA account, but neither of those was originally linked here so you wouldn't have any progress from them. They would just have access to whatever progress is already on this EA account.
If you're trying to restore progress, you would need to link your platforms to their original EA accounts and try accessing it there. There is not a way to transfer progress from one EA account to another, so if you have progress split across multiple EA accounts as appears to be the situation here, there won't be a way to merge that together I'm afraid.