SteamOS is on the verge of huge growth to its player base with the Steam Machine's arrival, and that's why this one factor can't be ignored by game developers.
You can use Heroic to manage Epic Store games. It’s not that hard to use on Linux. I rarely do it, but it’s easy. I don’t see why anything would prevent Linux users from playing it.
Numbers is the only way to speak to the bean counters making the decisions. They don’t care otherwise. Need more Linux users.
With the game removed from the store and the fact they sold out to Epic I doubt Rocket League will be getting many more Linux players.
People who bought the game on steam can still play from there but also EG works on Linux (source: I play from Linux)
You can use Heroic to manage Epic Store games. It’s not that hard to use on Linux. I rarely do it, but it’s easy. I don’t see why anything would prevent Linux users from playing it.