Epic Games just bought Psyonix, the developer of Rocket league, this will mean that Rocket League will be available on the epic game store relatively soon. The developer has already addressed the rumor that it would be removed off steam by saying that the game will remain on the steam store as well.
Rocket league said on their site the following about Epic:
Rocket League always has been and always will be a community-driven game, and now that we have joined forces with Epic, we will be able to serve our community in even bigger and better ways!
They also had the following thing to say about the e-sports ecosystem, that plays a big part in the Rocket League community:
We think this is a great move for the Rocket League Esports ecosystem because it significantly increases our potential reach and resources, just like it does for the game itself. We really do believe that you’ll find our future in esports to be very exciting — especially in the near future, where on June 21-23 at the Prudential Center in Newark, New Jersey, the Rocket League Championship Series (RLCS) finals will end our 7th season with a bang!
Rocket League came out back in 2015 for free with PlayStation Plus and started out with a massive playercount because of that. It also came out later for PC and Xbox.
Source: Rocket League