This was to be expected, when Epic Games, notorious for not giving a rat's ass about Linux support, acquired the studio behind Rocket League. Other titles from studios bought by Epic will likely follow if they have not already.
This does pose the question on what happens to Linux players who have invested into digital purchases. Online functionality will be disabled so all items will basically be void and the game becomes mostly worthless.
I also wonder if this means that Rocket League will not run on Google Stadia and its competitors, as those platforms mostly run on Linux systems.
Is there any major studio or publisher that DOES give a rat's ass about Linux gaming?
Valve
When was the last time they actually released a game though? From Wikipedia I can see:
Nov 2018 - Artifact (Collectible card game on Windows/Linux/MacOS)
Apr 2016 - The Lab (Windows only)
Dec 2014 - Left 4 Dead: Survivors (Arcade game?)
Oct 2014 - Counter-Strike Nexon: Zombies (Windows only)
2013 - Counter-Strike Online 2 (Windows only)
Heck even their new tentpole title Half-Life: Alyx is Windows only. Those aren't really big Linux credentials to boast about.