I always added packs from ea app, why do the purchase goes through epic games?

Hi.

I started playing sims 4 when base game became free on epics game, since then, I've purchased packs and kits and so, directly from the ea app. Whenever I played the game, I always opened ea app, click play and it automatically opened epic games by itself, so whenever I wanted a pack, I bought it from ea cause it was always open on my computer. The thing is, I heard steam is "better" than epic, so I deleted epic games and tried to play it using steams but the packs are gone? There is nothing in ea app, so I searched my emails and realized the receipts were emailed to epic games account. I wanna know why they went through epic if I was always using the ea app? Is there a way I can transfer packs to steam, in a way that allows me to delete epic games app too? Don't have to explain me how, I just wanted to try steam but I don't think it's worth it if I also have to keep epic games app... But still curious to why my packs don't belong in my ea account.

More info just in case:

I'm using the same ea account I first created, I don't even have more than one. The "purchase history" it's empty on my ea account. Don't even see an option to link epic games to ea, but there's an option to link to steam. Packs I owned showed "not owned" and gave me the option to buy on the ea app. I didn't delete anything else just epic games app from my computer.