The Epic Games Store became the Windows download home for new Rocket League players after the game went free-to-play. The transition happened on September 23, 2020, following Epic Games’ acquisition of developer Psyonix in 2019.
Before the change, the Windows version was sold and downloaded through Steam. When free-to-play launched, Rocket League was removed from new Steam sales and made available through the Epic Games Store instead. This made Epic’s storefront the standard destination for new PC players.
Existing Steam owners were not abandoned: they could continue downloading, updating, and playing their copy through Steam, including cross-platform multiplayer. That distinction explains why both Steam and Epic may appear in discussions about Rocket League on Windows, even though only the Epic Games Store became the new-player storefront.