What does the launcher do with regard to the operation of the game that cannot be done within the actual game itself? Is it due to a technical limitation or simply there for the convenience of the players? Are there alternatives to such methods of starting the execution of games?
Other than a handful of games where it does literally nothing but force you to sign in to something (such as Rockstar’s Social Club shit or the Xbox Live for Windows thing from years past) most of the ones I see having a launcher just for the one game are ones that let you adjust settings before starting, choose a renderer version to use (Vulkan, DX11, or DX12, etc), or, like as is with Minecraft, allows you to have a safe modded version kept separate from your vanilla game or to manage saves.
You can also, in most cases, bypass those launchers by just launching the preferred executable in the game’s installation directory.
Ah yes, if you’ve ever had the problem of a game’s graphics not working properly but you can’t adjust the graphics because it requires you to launch the actual game and navigate the settings menu you will appreciate that. Most games store and read their settings in an external file and a launcher can provide a meaningful way to edit those. That being said there’s many launchers who actually don’t offer this feature and are just used to shove ads your way or track your behavior.