I bought The Division 2 after seeing a promotion on the Epic store. To install it, you have to install the Ubisoft store Uplay, which is launched through an integration with the Epic store.

After playing that game, I saw promotions for Assassin's Creed Odyssey on Uplay, and purchased it. I later went on to purchase many other games on Uplay.

In short, Epic allows Ubisoft to sell games on its store, for which they presumably pay a cut - for those sales. But Epic has no problems letting Ubisoft require their store be installed for those games, and if you buy something there - even though the Epic Launcher installed it - they don't get a cut.

This is more akin to the App Store installing Fortnite - which Apple could get a cut out of, but not getting a cut for purchases in the app.