Why, when purchasing TSW4 from Epic Games, the additions from the previous parts were not transferred? from steam, there is only the game and standard DLC, nothing else.
Steam, Epic, Microsoft and Playstation are all competitors. None of them want you to buy from the others and that's why DLC doesn't work cross-platform. So everything you own should be on one platform. If you have DLC for one platform but not the other, you have to buy it again on the other platform. That's life. EDIT: I also can't understand or comprehend why you bought TSW 4 on Epic when you already own so much DLC on Steam.. That's totally illogical..
No other game lets you transfer content between epic and steam. Like above said, they are competing against each other and different platforms.