After being bought by Epic Games, creator of Fortnite, Rocket League is now being changed to a free-to-play model:

The update will also coincide with the game’s debut on the Epic Games Store and its removal from Steam. Psyonix said that Steam players will still get updates and will be able to play with those on other platforms — Rocket League is available on Nintendo Switch, PlayStation 4, Windows PC, and Xbox One — after the change.

The free-to-play model works great for me because I'm very rarely tempted to spend any money on the games. I've managed to play Fortnite (poorly) for a few years without spending a dollar.

Unfortunately my $0 is being counter-balanced by my kids who buy a Battle Pass once every few months.