It's not just major publishers that have their own launchers.
The creators of the Russian turn-based tactics game "Sparta 2035" are preparing for the release of the full version of the game.
They recently announced the release date and also announced the termination of support for the game launcher.
You don't need to buy the game a second time — the authors will provide a Steam key:
Everyone who bought Sparta through the launcher has access to a Steam key for the game on our website on the "My Games" page
The developers explained that "the cancellation of the launcher is not related to finances, but to priorities, we are still a small team, and supporting the launcher has become too resource-intensive, the priority is on game development!".
You can add "Sparta 2035" to your wishlist on Steam via the following link.